Force-measuring device testing system, force-measuring device calibration system, and a method of calibrating a force-measuring device

ABSTRACT

A force-measuring device testing system is disclosed. A linear actuator assembly includes a Z-axis actuator and a slider. A load cell is secured to the slider, such that actuation of the Z-axis actuator is mechanically coupled to a vertical movement of the load cell via the slider. The load cell is configured to impart a time-varying applied force to the sample which includes a force-measuring device. A load cell signal processing circuitry is configured to measure force signals at the load cell and output amplified force signals to the controller. The controller is configured to repeatedly carry out the following until a desired force trajectory has been executed: (1) calculate digital force signals in accordance with the amplified force signals, (2) calculate a next actuation of the Z-axis actuator in accordance with a desired force trajectory and an elastic parameter, and (3) control the actuation of the Z-axis actuator in accordance with its next calculated actuation.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional PatentApplication No. 62/991,433 filed on Mar. 18, 2020, entitledFORCE-MEASURING DEVICE TESTING SYSTEM, FORCE-MEASURING DEVICECALIBRATION SYSTEM, AND A METHOD OF CALIBRATING A FORCE-MEASURINGDEVICE, which is incorporated herein in its entirety.

BACKGROUND

With advancements in microelectromechanical systems (MEMS) technologies,it has become possible to fabricate MEMS chips containing piezoelectricmicromechanical force-measuring elements (PMFEs). MEMS chips containingPMFEs are examples of force-measuring devices.

Electronic apparatuses incorporating force-measuring devices can bemanufactured. Accordingly, systems and methods for calibratingforce-measuring devices and systems and methods for mapping forcetransmission to force-measuring devices are desired.

SUMMARY OF THE INVENTION

In one aspect, a force-measuring device testing system includes: alinear actuator assembly including a Z-axis actuator and a slider, aload cell secured to the slider, and a sample stage configured to retaina sample including a force-measuring device. Actuation of the Z-axisactuator is mechanically coupled to a vertical movement of the load cellvia the slider.

In another aspect, the force-measuring device testing system includes acontroller and a load cell signal processing circuitry. The controlleris electronically coupled to the Z-axis actuator. The load cell signalprocessing circuitry is electronically coupled to the load cell and thecontroller and is configured to measure force signals at the load celland output amplified force signals to the controller. The load cell isconfigured to impart a time-varying applied force, during the verticalmovement of the load cell, to the sample. The controller is configuredto repeatedly carry out the following until a desired force trajectoryhas been executed: (1) calculate digital force signals in accordancewith the amplified force signals, (2) calculate a next actuation of theZ-axis actuator in accordance with a desired force trajectory and theelastic parameter; and (3) control the actuation of the Z-axis actuatorin accordance with its next calculated actuation.

In yet another aspect, a method of calibrating a force-measuring deviceis disclosed. The method includes the following: (A) configuring aforce-measuring device testing system, (B) configuring a sampleincluding a force-measuring device, (C) obtaining a desiredforce-trajectory, (D) operating the force-measuring device testingsystem, (E) reading, by a force-measuring device controller, a digitaltransducer data output from a signal processing circuitry of theforce-measuring device when the time-varying applied force is impartedto the sample; and (F) adjusting or selecting, by the force-measuringdevice controller, a gain of the force-measuring device in accordancewith the digital transducer data.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through examples, which examples can be used invarious combinations. In each instance of a list, the recited listserves only as a representative group and should not be interpreted asan exclusive list.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of a user-input system including twoforce-measuring and touch-sensing integrated circuits (FMTSICs).

FIG. 2 is a schematic cross-sectional view of a force-measuring device,implemented as a force-measuring and touch-sensing integrated circuit(FMTSIC).

FIG. 3 is a schematic cross-sectional view of a certain portion of theforce-measuring and touch-sensing integrated circuit (FMTSIC) of FIG. 2.

FIG. 4 is a schematic cross-sectional view of a piezoelectricmicromechanical force-measuring element (PMFE).

FIGS. 5, 6, and 7 are schematic side views of force-measuring andtouch-sensing integrated circuits (FMTSICs) and a cover layer, attachedto each other and undergoing deformation.

FIG. 8 is a schematic top view of a PMFE array of a force-measuringdevice.

FIG. 9 is a schematic top view of a MEMS portion of a force-measuringtouch-sensing integrated circuit (FMTSIC).

FIG. 10 is a schematic cross-sectional view of another force-measuringdevice.

FIG. 11 is a schematic cross-sectional view of a PMFE of theforce-measuring device of FIG. 10.

FIG. 12 is a schematic cross-sectional view of a MEMS device.

FIG. 13 is a schematic cross-sectional view of a PMFE of the MEMS deviceof FIG. 12.

FIG. 14 is an electronics block diagram of a force-measuring device.

FIG. 15 is an electronics block diagram of a force-measuring device,implemented as an FMTSIC.

FIG. 16 is a schematic view of another illustrative user-input systemhaving force-measuring and touch-sensing capabilities.

FIGS. 17, 18, and 19 are flow diagrams of methods of makingforce-measuring devices, making an electronic apparatus incorporatingthe force-measuring device, and calibrating the force-measuring deviceor mapping data of force transmission to the force-measuring device.

FIG. 20 is a schematic block diagram showing an arrangement of aforce-measuring device testing system, a force-measuring device, and aforce-measuring device controller.

FIG. 21 is a schematic block diagram showing an arrangement of aforce-measuring device testing system and an electronic apparatusincorporating a force-measuring device.

FIG. 22 is a schematic block diagram showing an arrangement of aforce-measuring device testing system and a force-measuring device.

FIG. 23 is a schematic perspective view of a force-measuring devicetesting system.

FIG. 24 is a schematic elevational view of load cells and associatedcomponents.

FIG. 25 is a schematic elevational view of an arrangement for testing aforce-measuring device.

FIG. 26 is a schematic elevational view of an arrangement for testing anelectronic apparatus incorporating a force-measuring device.

FIG. 27 is a schematic block diagram showing a mapping system formapping data of force transmission from a plurality of force-impartingpoints to each force-measuring device.

FIG. 28 is a flow diagram of a method of calibrating a force-measuringdevice.

FIG. 29 is a flow diagram of a method of obtaining a desiredforce-trajectory.

FIG. 30 is a flow diagram of a method of operating a force-measuringdevice testing system.

FIG. 31 is a flow diagram of a method of mapping data of forcetransmission from a plurality of force-imparting points to eachforce-measurement device.

FIG. 32 is a diagram showing graphical plots of a desired forcetrajectory, digital force signals, and digital transducer data.

FIG. 33 shows plots of data of force transmission from force-impartingpoints to each of the force-measuring devices.

FIG. 34 is a schematic top view of a MEMS portion of a force-measuringdevice used in the mapping of FIG. 33.

FIGS. 35, 36, and 37 are graphical plots of digital transducer datameasured at one of the force-measuring devices in response to forcesimparted at respective force-imparting points.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure relates to a force-measuring device testingsystem, a force-measuring device calibration system, and a method ofcalibrating a force-measuring device.

In this Disclosure:

The words “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful and is not intended to exclude other embodiments from the scopeof the invention.

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

Unless otherwise specified, “a,” “an,” “the,” and “at least one” areused interchangeably and mean one or more than one.

The recitations of numerical ranges by endpoints include all numberssubsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, 5, etc.).

For any method disclosed herein that includes discrete steps, the stepsmay be conducted in any feasible order. As appropriate, any combinationof two or more steps may be conducted simultaneously.

FIG. 20 is a schematic block diagram showing an arrangement of a testingsystem 600, a force measuring device 630, and a force-measuring devicecontroller 638. Generally, the testing system 600 can be referred to asa force-imparting system, used to impart a force to any sample. A samplemeans any test sample that can be tested in the testing system. When thesample includes the force-measuring device 630, the testing system 600can be referred to as a force-measuring device testing system. Forexample, a sample can be an electronic apparatus including a cover layerand at least one force-measuring device, with the cover layer attachedto the force-measuring device(s). Some examples of samples are asmartphone (640 of FIG. 26) and a touch-panel user-input system (500 ofFIG. 16). A combination of the force-measuring device testing system 600and the force-measuring device controller 638 is referred to as aforce-measuring device calibration system. For example, such acalibration system could be controlled from a computer 608.

An example of a testing system 600 is shown in perspective view in FIG.23. The testing system 600 includes a base 612, a support structure 614attached to the base 612, a linear actuator assembly 602 suspended bythe support structure 614, and a sample stage 626 mounted on the base612. In the example shown, the sample stage 626 includes a sample holder628. First load cell 616 (bottom load cell) and second load cell 618(top load cell) (collectively referred to as load cells 604) are securedto the slider 658. In the example shown, the support structure 614consists of two parts, the respective parts being located to the rightand to the left of the linear actuator assembly (along the X-axis 652).Both parts of the support structure 614 support the linear actuatorassembly 602. The linear actuator assembly 602 includes a Z-axisactuator 660 and a slider 658. In the example shown, the Z-axis actuator660 is a stepper motor. In the linear actuator assembly 602, a rotationof the Z-axis actuator 660 is converted into linear motion of a slider658 along a linear guide 668. As shown in FIG. 23, the slider 658 movesalong a vertical axis (Z-axis 656). In the example shown, the samplestage 626 includes a Y-axis positioner 624 mounted on top of an X-axispositioner 622 and the sample holder 628 mounted on top of the Y-axispositioner 624. The X-axis positioner 622 is shown to include an X-axisactuator 662. For example, if the sample holder 628 retains multiplesamples arrayed along the X-axis 652, the testing system can actuate theX-axis actuator 662 of the X-axis positioner 622 to displace each sampleto a specific location under the first load cell 616 for testing.

The load cells 604 and associated components are schematically shown inelevational view in FIG. 24. A top end of a first load cell 616 issecured to a first fixing element 676, which is secured to the slider658 (FIG. 23). Actuation of the Z-axis actuator 602 is mechanicallycoupled to a vertical movement (along the Z-axis 656) of the first loadcell 616 via the slider 658. A top end of a first elastic member 620 isattached to a bottom end of the first load cell 616, and a top end of asecond elastic member 664 is attached to a bottom end of the firstelastic member 620. During operation of the test system 600 in aforce-imparting mode, a bottom end 670 of the second elastic member 664is brought into contact with (impacts) a sample (e.g., a samplecontaining a force-measuring device). The first elastic member 620 andthe second elastic member 664 are arranged in series between the firstload cell 616 and the sample when the sample is retained in the sampleholder. In the example shown, the first elastic member 620 includes asteel spring and the second elastic member 664 is a rubber block. Thefirst elastic member is less elastic than the second elastic member. Wehave found that if no elastic member is inserted between the first loadcell 616 and the sample, the landing of the first load cell 616 on thesample is highly impulsive (for example, rapid change from negligibleforce to excessive force). Additionally, we have found that with acombination of a first elastic member (less elastic, such as a steelspring) and a second elastic member (more elastic, such as a rubberblock), the forces applied on the sample can vary gradually from minimumforce to maximum force. In the force-imparting mode, the first load cell616 is configured to impart a time-varying applied force to the sampleduring the vertical movement of the first load cell, the time-varyingapplied force being imparted via at least one elastic member positionedbetween the first load cell and the sample.

Additionally, a second load cell 618 can be used. A bottom end of thesecond load cell 618 is secured to a second fixing element 678, which issecured to the slider 658. Alternatively, the bottom end of the secondload cell can be secured to the first fixing element 676, in which caseno second fixing element is needed. The second load cell 618 is securedto the slider 658 such that actuation of the Z-axis actuator ismechanically coupled to a vertical movement (along the Z-axis 656) ofthe second load cell via the slider. Preferably, the first load cell 616and the second load cell 618 are chosen to have similar operatingcharacteristics (e.g., be of the same model number from the samemanufacturer). The first load cell 616 and the second load cell 618 areoriented in opposite directions along the vertical axis (Z-axis 656).The first load cell 616 has its top end secured to the slider while thesecond load cell 618 has its bottom end secured to the slider. If asecond load cell 618 is not used, the first load cell 616 is sometimessimply referred to as the load cell.

The testing system 600 includes a controller 606 and a load cell signalprocessing circuitry 610 (FIG. 20). The controller 606 is electronicallycoupled to the Z-axis actuator 660 of the linear actuator assembly 602.A load cell signal processing circuitry 610 is electronically coupled tothe load cells 604 (first load cell 616 and second load cell 618) andthe controller 606. The load cell signal processing circuitry 610preferably includes an instrumentation amplifier. The load cell signalprocessing circuitry 610 configured to measure first force signals atthe first load cell 616 and output first amplified force signals to thecontroller 606. If a second load cell is present, the load cell signalprocessing circuitry 610 is electronically coupled to the second loadcell and is configured to measure second force signals at the secondload cell 618 and output second amplified force signals to thecontroller 606.

When a first item is electronically coupled to a second item, there isan electronic signaling pathway, such as a wired connection or awireless connection, between the first and second items. An example of awired connection is a universal serial bus (USB) connection. In theexample shown, a computer 608 is electronically coupled to thecontroller 606 and a force-measuring device controller 638. Theforce-measuring device controller 638 is electronically coupled to theforce-measuring device 630. The force-measuring device controller 638supplies electrical power to the force-measuring device 630 andcommunicates with the force-measuring device 630.

FIG. 28 is a flow diagram of a method 800 of calibrating aforce-measuring device. Method 800 includes steps 802, 804, 806, 808,810, 812, and 814. At step 802, the force-measuring device testingsystem (testing system) 600 is configured. As discussed in detail above,the testing system 600 includes: (1) a linear actuator assembly 602including a Z-axis actuator 660 and a slider 658, (2) a first load cell616 secured to the slider 658, such that actuation of the Z-axisactuator 660 is mechanically coupled to a vertical movement of the firstload cell 616 via the slider 658, (3) a controller 606 electronicallycoupled to the Z-axis actuator 660, and (4) a load cell signalprocessing circuitry 610 electronically coupled to the first load cell616 and the controller 606, configured to measure first force signals atthe first load cell 616 and output first amplified force signals to thecontroller 606.

At step 804 of method 800, a sample stage, a sample including aforce-measuring device, and a force-measuring device controller areconfigured. The sample stage (626 of FIG. 23) retains the sample whichincludes at least one force-measuring device 630. Each force-measuringdevice 630 includes a signal processing circuitry. The force-measuringdevice controller 638 is electronically coupled to the signal processingcircuitry of each force-measuring device 630. Examples of possibleconfigurations are shown in FIGS. 25 and 26. In FIG. 25, twoforce-measuring device 630 are shown, mounted on a chip tester 682,which functions as a sample holder. The chip tester can be mounted tothe sample stage 626 (FIG. 23). The force-measuring device 630 can be apackaged integrated circuit (IC). The force-measuring device 630 cancontain piezoelectric micromechanical force-measuring elements (PMFEs).Chip tester 682 is electronically coupled, via connection 686, to theforce-measuring device controller 638. A direction in which a force fromthe first load cell is imparted is shown as arrow 688. This force isimparted to a cover layer 680, which is attached to the top surfaces offorce-measuring devices 630 via an adhesive layer 684.

In FIG. 26, two force-measuring devices 630A, 630B have been assembledin an electronic apparatus 640. In the example shown, the electronicapparatus 640 is a smartphone which includes a display 690,microprocessor (not shown in FIG. 26), and a memory (not shown in FIG.26). In the smartphone (or other electronic apparatus), the memory iselectronically coupled to the microprocessor. In the example shown, theelectronic apparatus 640 is retained by a sample holder 628. The sampleholder 628 can be mounted to the sample stage 626. The force-measuringdevices 630A, 630B have been incorporated into an interior of theelectronic apparatus 640. A direction in which a force from the firstload cell is imparted is shown as arrow 688. This force is imparted toan external housing 648 of the electronic apparatus 640. Preferably, theforce-measuring devices are attached to an interior surface of theexternal housing 648 via an adhesive layer. In this case, the externalhousing functions as a cover layer for the force-measuring devices.

In the example shown in FIG. 20, the force-measuring device 630 includespiezoelectric micromechanical force-measuring elements (PMFEs) 632,amplifiers 634, and analog-to-digital converters (ADCs) 636. Theamplifiers 634 and the ADCs 636 are referred to as signal processingcircuitry of the force-measuring device 630. When a time-varying forceis imparted by the first load cell 616 to the sample at aforce-imparting point: (1) there is a low-frequency mechanicaldeformation propagating in the sample as a result of the applied force;(2) the low-frequency mechanical deformation causes a strain at thePMFEs 632 and voltage signals are generated at the PMFEs 632 inaccordance with the strain; (3) amplifiers 634 amplify the voltagesignals output from the PMFEs 632 and the ADCs 636 convert the amplifiedvoltage signals from the amplifiers 634 to digital transducer data.Herein, when we refer to voltage signals output from the PMFEs, this mayrefer to voltage signals from a single PMFE, from multiple PMFEs, orfrom the outermost electrodes of PMFEs in a set of PMFEs connected inseries. Force-measuring device controller 638 is configured to read thedigital transducer data output from the signal processing circuitry ofthe force-measuring device(s), when the time-varying force is impartedto the sample. In the example shown in FIG. 20, the force-measuringdevice controller 638 reads the digital transducer data from the ADCs636. As explained hereinbelow, the force-measuring device controller 638adjusts or selects the gain of the force-measuring device 630 inaccordance with the digital transducer data.

At step 806, a desired force-trajectory is obtained. FIG. 29 is a flowdiagram of an example method of obtaining the desired force-trajectoryby manual force input, such as a force input by a finger (e.g., fingerpress) at the second load cell 618. In the example shown, step 806includes sub-steps 840, 842, 844, 846, and 848. In this manual inputmode, the second load cell 618 is used. At sub-step 840, the second loadcell 618 receives a manual force input while the first load cell 616,the second load cell 618, and the slider 658 are configured to bestationary during the manual input mode. For example, the actuator 660is turned off and the slider does not move. For example, the manualforce input includes a finger pressing against the second load cell 618from the top. At sub-step 842, the load cell signal processing circuitry610 measures second force signals at the second load cell and amplifiesthe second force signals. At sub-step 844, the load cell signalprocessing circuitry 610 outputs second amplified force signals to thecontroller 606. At sub-step 846, the controller obtains digital forcesignals in accordance with the second amplified force signals. Forexample, this can include converting the second amplified force signalsto digital signals. At sub-step 848, the controller determines thedesired force trajectory in accordance with the digital force signals.For example, the controller can determine the digital force signals tobe the desired force trajectory or can carry out additional signalprocessing on the digital force signals. The desired force trajectorycan be stored in a memory store for subsequent retrieval and use.Accordingly, after the desired force trajectory has been measured (forexample, according to FIG. 29) and stored, step 806 can includeretrieving a previously recorded desired force trajectory. Furthermore,the desired force trajectory can be constructed digitally or can bemeasured at another force sensor different from the second load cell618.

At step 808, the testing system 600 is operated. Step 808 of operatingthe testing system 600 is explained in greater detail in FIG. 30. Step808 includes sub-steps 850, 852, 854, 856, 858, 860, 862, and 864. Atsub-step 850, the controller calculates an actuation of the Z-axisactuator in accordance with the desired force trajectory and an elasticparameter. The controller calculates the number of steps of the steppermotor in the stepper motor's next iteration (cycle). An example of adesired force trajectory is shown in FIG. 32, which shows graphicalplots of a desired force trajectory, digital force signals, and digitaltransducer data. The graphical plots have a horizontal axis 902 whichshows time t, in which 1 box corresponds to 500 ms, and a vertical axis904 which shows force. FIG. 32 is an example output 900 of a userinterface on the computer 608. FIG. 32 shows a desired force trajectory910 (data points shown as circles) which is a sinusoidal wave with anamplitude of 7.5 N and a frequency of 5 Hz. In addition, there is aninterval period of 50 ms between adjacent periods at the minimumamplitude. In the case of the desired force trajectory 910, 1 box alongthe vertical axis 944 corresponds to 5 N. In this case, the desiredforce trajectory is set by an operator via the user interface on thecomputer 608. Alternatively, the desired force trajectory can be set bythe manual input mode shown in FIG. 29. The elastic parameter is anumerical parameter that relates actuation of the Z-axis actuator 660 toa time-varying applied force at the first load cell 616 resulting fromthat actuation (measured as digital force signals). It is preferablethat the time-varying applied force closely approximate the desiredforce trajectory 910 (the deviation of the digital force signals fromthe desired force trajectory be kept small). Preferably, the elasticparameter is updated by the controller in real-time.

At sub-step 852, the controller controls an actuation of the Z-axisactuator in accordance with the calculated actuation (from sub-step850). In the case that the Z-axis actuator is a stepper motor, thecontroller controls the stepper motor in accordance with its calculationof the number of steps of the stepper motor in the stepper motor's nextiteration (cycle). The rotation of the stepper motor causes verticalmovement of the load cells (first load cell 616 and second load cell618). At sub-step 854, the first load cell 616 imparts a time-varyingapplied force to the sample (which includes force-measuring device 630)during its vertical movement. The time-varying applied force is impartedvia at least one elastic member (620 and/or 664) positioned between thefirst load cell 616 and the sample.

At sub-step 856, the load cell signal processing circuitry 610 measuresfirst force signals at the first load cell 616 and amplifies the firstforce signals (first amplified force signals). Optionally, the load cellsignal processing circuitry 610 measures second force signals at thesecond load cell 618 and amplifies the second force signals (secondamplified force signals). Preferably, the load cell signal processingcircuitry 610 includes instrumentation amplifiers which amplify thefirst force signals measured at the first load cell 616 and amplify thesecond force signals measured at the second load cell 618. At sub-step858, the load cell signal processing circuitry 610 outputs firstamplified force signals to the controller 606. Optionally, the load cellsignal processing circuitry 610 outputs second amplified force signalsto the controller 606.

At sub-step 860, the controller 606 calculates digital force signals inaccordance with the first amplified force signals. For example, thecontroller 606 includes ADCs that convert the first amplified forcesignals into first digital force signals. In the case that the signalprocessing circuitry 610 does not output second amplified force signalsto the controller 606, the first digital force signals can be referredto simply as digital force signals. For example, the signal processingcircuitry 610 additionally outputs second amplified force signals to thecontroller 606, the controller 606 also converts the second amplifiedforce signals to second digital force signals, and the controller 606subtracts the second digital force signals from the first digital forcesignals to obtain the digital force signals. In this case, thecontroller is configured to convert the first amplified force signals tofirst digital force signals; convert the second amplified force signalsto second digital force signals; and subtract the second digital forcesignals from the first digital force signals to obtain the digital forcesignals. Accordingly, some of the inertial forces arising from theacceleration or deceleration of the first load cell can be canceled.

FIG. 32 shows an example of digital force signals 912 (data points shownas squares). In the case of the digital force signals 912, 1 box alongthe vertical axis 904 corresponds to 5 N (same scale as the desiredforce trajectory 910). A digital force signal range 922 of the digitalforce signals 912 is the difference between the maximum and the minimumdigital force signals. In the example shown, the digital force signalrange 922 is approximately 7.5 N. In the example shown, the deviation ofdigital force signals 912 from the desired force trajectory 910 is quitesmall (the digital force signals 912 closely track the desired forcetrajectory). It is preferable that the controller be capable of updatingthe elastic parameter. It is preferable that the controller beconfigured to update the elastic parameter in accordance with adeviation of the digital force signals from the desired forcetrajectory. When the deviation of digital force signals 912 from thedesired force trajectory 910 is relatively small, the controller canmake a relatively small adjustment to the elastic parameter. When thedeviation of digital force signals 912 from the desired force trajectory910 is relatively large, the controller can make a relatively largeadjustment to the elastic parameter. Accordingly, at sub-step 862, thecontroller updates the elastic parameter in accordance with a deviationof the digital force signals from the desired force trajectory.Sub-steps 850, 852, 854, 856, 858, 860, and optionally 862 are repeateduntil the desired force trajectory has been completed (decision sub-step864). Each data point of the digital force signals 912 corresponds toone iteration of the sequence of sub-steps 850, 852, 854, 856, 858, 860,and optionally 862.

At step 810, the force-measuring device controller 638 reads the digitaltransducer data output from the signal processing circuitry of theforce-measuring device 630 when the time-varying applied force isimparted to the sample. FIG. 32 shows an example of digital transducerdata 914 (data points shown as triangles). Each data point of thedigital transducer data 914 corresponds to one reading of the digitaltransducer data output by the force-measuring device controller 638. Theforce-measuring device controller 638 reads the digital transducer datamultiple times for each sinusoidal wave period of the desired forcetrajectory 910. In the case of the digital transducer data 914, 1 boxalong the vertical axis 904 corresponds to 500 LSB. A digital transducerdata range 924 of the digital transducer data 914 is the differencebetween the maximum and the minimum digital transducer data. In theexample shown, the digital transducer data range 924 is approximately1300 LSB, which can also be expressed as ±650 LSB.

At step 812, the force-measuring device controller 638 adjusts orselects a gain of the force-measuring device 830 in accordance with thedigital transducer data. In the example shown, the digital force signalshave a range of approximately 7.5 N, closely tracking a range of 7.5 Nof the desired force trajectory. As the applied force varies with time,an increase in the force to the maximum (+7.5 N relative to the minimum)may represent a digit pressing against the force-measuring device and adecrease in the force to the minimum may represent the digit beinglifted away from the force-measuring device. In the example shown, anoutput range of the signal processing circuitry of the force-measuringdevice is 2048 LSB, and a range of the desired force trajectory is 7.5N. Depending upon a desired range of the digital transducer data, theforce-measuring device controller adjusts or selects a gain of theamplifier 634. Suppose for example that the desired range of the digitaltransducer data is ±650 LSB, under a standard time-varying applied forceof 7.5 N. The time-varying applied force is repetitively applied whilean adjustable or selectable gain of the amplifier 634 is set at G1, G2,and G3. At gain G1, the range of the digital transducer data is measuredto be ±610 LSB, at gain G2, the range of the digital transducer data ismeasured to be ±640 LSB, and at gain G3, the range of the digitaltransducer data is measured to be ±700 LSB. The force-measuring devicecontroller may set the adjustable or selectable gain at G2 if a measuredrange of ±640 LSB is satisfactory (i.e., sufficiently close to ±650LSB). If the measured range of ±640 LSB is not satisfactory, theforce-measuring device may calculate another gain intermediate betweenG2 and G3 that is expected to be satisfactory and set the adjustable orselectable gain at that intermediate gain value.

Step 814 is an optional step, at which the force-measuring devicecontroller calculates and stores calibration data in the force-measuringdevice. This calibration data may include: (1) a ratio A of acharacteristic amplitude of the digital transducer data to acharacteristic amplitude of the digital force signals; and/or (2) aratio B of a characteristic amplitude of the digital force signals to acharacteristic amplitude of the digital transducer data. Acharacteristic amplitude of the digital transducer data may be a rangeof the digital transducer data. A characteristic amplitude of thedigital force signals may be a range of the digital force signals. Forexample, if a range of the digital force signals is 7.5 N and a range ofthe digital transducer data is 1280 LSB (±640 LSB), then the ratioA=1280 LSB/7.5 N and the ratio B=7.5 N/1280 LSB. These ratios A and Bpermit a conversion of digital transducer data (expressed in LSB) to aphysical force value (expressed in Newtons) and vice versa.

Accordingly, the force-measuring device controller 638 is configured to:(1) read digital transducer data output from the signal processingcircuitry of the force-measuring device(s) 630 when the time-varyingapplied force is imparted to the sample; and (2) adjust or select a gainof the force-measuring device(s) 630 in accordance with the digitaltransducer data. Optionally, the force-measuring device controller isconfigured to calculate calibration data and store the calibration datain the force-measuring device. The calibration data can include: (1) aratio of a characteristic amplitude of the digital transducer data to acharacteristic amplitude of the digital force signals; and/or (2) aratio of a characteristic amplitude of the digital force signals to acharacteristic amplitude of the digital transducer data.

In the force-imparting mode, the controller is configured to repeatedlycarry out the following until a desired force trajectory has beenexecuted: (1) calculate digital force signals in accordance with theamplified force signals; (2) calculate a next actuation of the Z-axisactuator in accordance with the desired force trajectory and an elasticparameter; and (3) control the actuation of the Z-axis actuator inaccordance with its next calculated actuation. The elastic parameterrelates actuation of the Z-axis actuator to digital force signalsresulting from the actuation. Preferably, the controller is configuredto update the elastic parameter in accordance with a deviation of thedigital force signals from the desired force trajectory.

The first load cell 616 is configured, in the force-imparting mode, toimpart a time-varying applied force, during the vertical movement of thefirst load cell 616, to the sample including the force-measuring device630. The time-varying applied force is imparted via at least one elasticmember positioned between the first load cell 616 and the sample.

The load cell signal processing circuitry 610 is configured to measurefirst force signals at the first load cell 616 and output firstamplified force signals to the controller 606. Optionally, the load cellsignal processing circuitry 610 is configured to measure second forcesignals at the second load cell 618 and output second amplified forcesignals to the controller 606.

In the arrangement shown in FIG. 20, the force-measuring devicecontroller 638 supplies power to the force-measuring device 630 andadjusts or selects a gain of the force-measuring device. As shown inFIG. 26, the force-measuring device 630 can already be incorporated intoan electronic apparatus 640. In such case, an arrangement shown in FIG.21 may be possible. FIG. 21 shows a testing system 600 identical to thatshown in FIG. 20. In FIG. 21, the sample retained by the sample stage isan electronic apparatus 640 which includes the force-measuring device630. The electronic apparatus 640 includes a microprocessor 644 and amemory 642 electronically coupled to the microprocessor 644. Themicroprocessor functions as the force-measuring device controller. Asoftware program stored in the memory 642 is executed by themicroprocessor 644 for the microprocessor 644 to function as aforce-measuring device controller. In the arrangement shown in FIG. 21,a force-measuring device testing system 600 in combination with anelectronic apparatus 640 that includes a force-measuring device 630 anda microprocessor 644 that functions as a force-measuring devicecontroller can carry out the force-measuring device calibration method800 (FIG. 28).

FIG. 22 shows another arrangement of a force-measuring device testingsystem 600 and a force-measuring device 630. FIG. 22 shows a testingsystem 600 identical to that shown in FIG. 20. The force-measuringdevice 630 additionally includes a microcontroller 646 and a memory 645electronically coupled to the microcontroller 646. The microprocessorfunctions as the force-measuring device controller. A software programstored in the memory 645 is executed by the microcontroller 646 for themicrocontroller to function as a force-measuring device controller. Inthe arrangement shown in FIG. 22, the force-measuring device requires anexternal apparatus (not shown) that supplies electrical power andestablishes communication with it in order to operate.

FIG. 27 is a schematic block diagram of a system 700 for mapping data offorce transmission from a plurality of force-imparting points to eachforce-measuring device. Mapping system 700 includes a testing system600, a computer 608, and a force-measuring device controller 638. FIG.27 shows a testing system 600 identical to that shown in FIG. 20. Thecomputer 608 is electronically coupled to the controller 606 (of thetesting system 600) and the force-measuring device controller 638.Testing system includes a sample stage 626 which retains a sample 702.For example, the sample 702 can be an electronic apparatus thatincorporates at least one force-measuring device, such as a smartphoneor a touch-panel user-input system 500 (FIG. 16). Sample stage 626includes a sample stage positioner (e.g., X-axis positioner and Y-axispositioner) which positions the sample at specific positions along theX-axis 652 and Y-axis 654. The sample stage positioner positions thesample 702 at specific positions relative to the first load cell 616,such that in the force-imparting mode, the first load cell 616 imparts aforce to the sample 702 at one of multiple force-imparting points 704(shown as circles). In FIG. 27, a cover layer of the sample 702 isvisible. This could be an external housing of an electronic apparatus,for example. In the force-imparting mode, the first load cell 616imparts a time-varying applied force to the sample 702. The time-varyingapplied force is imparted via at least on elastic member positionedbetween the first load cell 616 and the sample 702. In the exampleshown, the sample 702 includes three force-measuring devices 630A, 630B,630C positioned behind and attached to the cover layer. Some of theforce-imparting points 706 do not overlap any of the force-measuringdevices (are laterally displaced from the force-measuring devices) andsome of the force-imparting points 708 overlap a respective one of theforce-measuring devices. Each of the force-measuring devices (630A,630B, 630C) includes a signal processing circuitry and theforce-measuring device controller is electronically coupled to thesignal processing circuitry of each force-measuring device.

FIG. 31 is a flow diagram of a method 870 of mapping data of forcetransmission from a plurality of force-imparting points to eachforce-measurement device. System 700 shown in FIG. 27 is used. Method870 includes steps 802, 874, 806, 876, 808, 810, 878, and 880. At step802, the force-measuring device testing system (testing system) 600 isconfigured. Step 802 has been described with reference to FIG. 28.

At step 874, a sample stage, a sample including a force-measuringdevice, and a force-measuring device controller are configured. Thesample stage 626 includes a sample stage positioner (e.g., X-axispositioner and Y-axis positioner) which positions the sample at specificpositions along the X-axis 652 and Y-axis 654. The sample stagepositioner positions the sample 702 at specific positions relative tothe first load cell 616, such that in the force-imparting mode, thefirst load cell 616 imparts a force to the sample 702 at one of multipleforce-imparting points 704. The sample stage (626 of FIG. 27) retainsthe sample 702 which includes at least one force-measuring device (630A,630B, 630C). Each force-measuring device 630A, 630B, 630C includes asignal processing circuitry. The force-measuring device controller 638is electronically coupled to the signal processing circuitry of eachforce-measuring device 630.

At step 806, a desired force-trajectory is obtained. Step 806 has beendescribed with reference to FIGS. 28 and 29. As discussed, FIG. 29 is aflow diagram of an example method of obtaining the desiredforce-trajectory by manual force input, such as a force input by afinger at the second load cell. After the desired force trajectory hasbeen measured (for example, according to FIG. 29) and stored, step 806can include retrieving a previously recorded desired force trajectory.Furthermore, the desired force trajectory can be constructed digitallyor can be measured at another force sensor different from the secondload cell 618.

At step 876, the controller controls actuation of the sample stagepositioner to position the first load cell 616 at each one of aplurality of force-imparting points 704 on the sample 702. For eachrespective force-imparting point, steps 808, 810, 878, and 880 arecarried out. Steps 808, 810, and 878 are carried out repeatedly untilall of the force-imparting points 704 have been tested (decision step880). At step 808, the testing system 600 is operated. Step 808 has beendescribed with reference to FIGS. 28 and 30. At step 810, theforce-measuring device controller 638 reads the digital transducer dataoutput from the signal processing circuitry of the force-measuringdevice 630 when the time-varying applied force is imparted to the sampleat each force-imparting point 704. Step 810 has been described withreference to FIG. 28. At step 878, a map of data of force transmissionfrom the plurality of force-imparting points 704 to the force-measuringdevice (630A, 630B, and/or 630C) is generated in accordance with digitaltransducer data obtained from of the force-measuring device (630A, 630B,and/or 630C) upon the imparting of the time-varying applied force ateach respective force-imparting point 704. When a force is imparted to asample at a force-imparting point, there is a low-frequency mechanicaldeformation propagating in the sample which causes a respective strainat the PMFEs of the force-measuring devices and digital transducer dataare obtained from the force-measuring devices in accordance with therespective strain.

FIG. 33 shows three two-dimensional plots 950, 960, and 970. Each plot(950, 960, 970) is a map of data of force transmission from a pluralityof force-imparting points (952, 962, 972) to a respectiveforce-measuring device (630A, 630B, 630C). The locations of theforce-measuring devices are marked by rectangles that represent theapproximate lateral dimensions of each force-measuring device. Theforce-measuring devices are attached, via an adhesive to a cover layer,which is a plastic frame in this example. The plastic frame is mountedto the sample stage 626. There are approximately 17 rows and 81 columnsof force-imparting points in each plot. All of the force-impartingpoints are on the plastic frame. The force-imparting points extend overan area measuring approximately 40 mm (along X-axis 982) by 8 mm (alongY-axis 984). There is a data point at the location of eachforce-imparting point. Each data point is either a circle or a triangle.A circle represents a first polarity of the digital transducer data anda triangle represents a second polarity of transducer data opposite thefirst polarity. The size of the circle or triangle represents acharacteristic amplitude of the digital transducer data. For example,plot 950 is a map of data of force transmission from force-impartingpoints 952 to the force-measuring device 630A (locations of otherforce-measuring devices 630B and 630C are shown for illustration only).A shape (circle or triangle) at each force-imparting point 952represents (1) a polarity of the digital transducer data obtained fromforce-measuring device 630A and (2) a characteristic amplitude of thedigital transducer data obtained from force-measuring device 630 uponthe imparting of the time-varying applied force at the respectiveforce-imparting point 952.

FIG. 34 is a schematic top view of a specific implementation of aforce-measuring device 630, used as force-measuring devices 630A, 630B,and 630C in the mapping shown in FIG. 33. In this example, theforce-measuring device is implemented as a packaged integrated circuit(IC) with lateral dimensions of approximately 2.6 mm along its longdirection 986 and approximately 1.4 mm along its short direction 988.There are four piezoelectric micromechanical force-measuring elements(PMFEs) (1000, 1001, 1002, 1003) near the four corners and an array 994of piezoelectric micromechanical ultrasonic transducers (PMUTs). ThesePMUTs are configured to have a touch-sensing functionality. Accordingly,this force-measuring device can be referred to as a force-measuring andtouch-sensing IC (FMT SIC). In the mapping shown in FIG. 33, the digitaltransducer data obtained from the force-measuring device is a sum of thedata at the four PMFEs (1000, 1001, 1002, 1003).

Plot 950 is a map of data of force transmission from force-impartingpoints 952 to the right force-measuring device 630A. For someforce-imparting points 954 near the force-measuring device 630A, thedata points are circles (first polarity) and for some force-impartingpoints 956 remote from the force-measuring device 630A the data pointsare triangles (second polarity). FIG. 35 is graphical plot 1010 ofdigital transducer data measured at the force-measuring device 630A inresponse to a time-varying applied force imparted at one of the nearforce-imparting points 954, specifically force-imparting point locatedat row 9, column 16. The rows (every 5 rows) are labeled to the right ofplot 950 and the columns (every 5 columns) are labeled at the top ofplot 950. This force-imparting point overlaps force-measuring device630A. The time-varying applied force consists of repetitively pressing,by the first load cell, against the force-imparting point five times.Plot 1010 has a horizontal axis 902 which shows time t and a verticalaxis 904 which shows force (digital transducer data). Before theapplication of the time-varying applied force, the PMFEs are in aquiescent state (plot section 1012). As the time-varying applied forcebegins, the digital transducer data show a positive slope (plot section1014) and then reaches a maximum 1016, corresponding to strain of afirst polarity at the PMFEs. This corresponds to the PMFEs under tension(see PMFE 146 in FIG. 5). As the pressure at the force-imparting pointis released, the digital transducer data decreases from a maximum 1016to a minimum 1018. Local maxima are reached five times, correspondingrepetitively pressing against the force-imparting point five times. Acharacteristic amplitude of the digital transducer data can be definedto be a difference between a local maximum 1016 and a local minimum1018. Alternatively, a characteristic amplitude of the digitaltransducer data can be defined to be a difference between a globalmaximum and a global minimum, within a predetermined time window such asshown in FIG. 35.

FIG. 36 is graphical plot 1020 of digital transducer data measured atthe right force-measuring device 630A in response to a time-varyingapplied force imparted at one of the remote force-imparting points 956,specifically force-imparting point located at row 1, column 38. Thisforce-imparting point corresponds to one of the large triangles abovemiddle force-measuring device 630B. The time-varying applied forceconsists of repetitively pressing, by the first load cell, against theforce-imparting point five times. Plot 1020 has a horizontal axis 902which shows time t and a vertical axis 904 which shows force (digitaltransducer data). Before the application of the time-varying appliedforce, the PMFEs are in a quiescent state (plot section 1022). As thetime-varying applied force begins, the digital transducer data show anegative slope (plot section 1024) and then reaches a local minimum1028, corresponding to strain of a second polarity at the PMFEs. Thiscorresponds to the PMFEs under compression (see PMFE 146A in FIG. 5). Asthe pressure at the force-imparting point is released, the digitaltransducer data increases from a local minimum 1028 to a local maximum1026. Local minima are reached five times, corresponding repetitivelypressing against the force-imparting point five times. A characteristicamplitude of the digital transducer data can be defined to be adifference between the local maximum 1026 and the local minimum 1028.Alternatively, a characteristic amplitude of the digital transducer datacan be defined to be a difference between a global maximum and a globalminimum, within a predetermined time window such as shown in FIG. 36.

In plot 950, there is a narrow region (band) of force-imparting points958, located between the near force-imparting points 954 and remoteforce-imparting points 956, for which the characteristic amplitudes arequite small. In this band of force-imparting points, there is atransition between force-imparting points of a first polarity and of asecond polarity. FIG. 37 is used to explain this transition. FIG. 37shows graphical plots of digital transducer data measured at the rightforce-measuring device 630A in response to a time-varying applied forceimparted at the following force-imparting points: plot 1030 correspondsto a force-imparting point at row 5, column 24, plot 1040 corresponds toa force-imparting point at row 5, column 23, and plot 1050 correspondsto a force-imparting point at row 5, column 22. Plots 1030, 1040, and1050 have characteristic amplitudes that are quite small compared toplots 1010 (FIGS. 35) and 1020 (FIG. 36). Plot 1030, corresponding to aforce-imparting point farthest from force-measuring device 630A, shows asecond polarity (triangles), and plot 1050, corresponding to aforce-imparting point closest to force-measuring device 630A, shows afirst polarity (circles). Amplitudes in plot 1040 are small enough thatit is difficult to discern the polarity. There is a transition betweenthe polarities at or near the force-imparting point corresponding toplot 1040.

Plot 960 is a map of data of force transmission from force-impartingpoints 962 to the middle force-measuring device 630B. For someforce-imparting points 964 near the force-measuring device 630B, thedata points are circles (first polarity) and for some force-impartingpoints 956 remote from (and generally to the left of) theforce-measuring device 630B the data points are triangles (secondpolarity). There is a narrow region (band) of force-imparting points968, located between the near force-imparting points 964 and remoteforce-imparting points 966, for which the characteristic amplitudes arequite small. In this band of force-imparting points, there is atransition between force-imparting points of a first polarity and of asecond polarity.

Plot 970 is a map of data of force transmission from force-impartingpoints 972 to the left force-measuring device 630C. For someforce-imparting points 974 near the force-measuring device 630C, thedata points are circles (first polarity) and for some force-impartingpoints 976 remote from (and generally to the left of) theforce-measuring device 630C the data points are triangles (secondpolarity). There is a narrow region (band) of force-imparting points978, located between the near force-imparting points 974 and remoteforce-imparting points 976, for which the characteristic amplitudes arequite small. In this band of force-imparting points, there is atransition between force-imparting points of a first polarity and of asecond polarity.

In plot 950, there is a region of remote force-imparting points(approximately bounded by boundary 940) from which there is significantforce-transmission to the force-measuring device 630A.

This significant force-transmission may be attributed to mechanicalcharacteristics of the cover layer (e.g., housing) to which theforce-measuring devices 630A, 630B, 630C are attached to which atime-varying force is imparted. For example, such mechanicalcharacteristics can include (1) shape, thickness, and/or rigidity of thecover layer or (2) another element to which the cover layer ismechanically coupled. In this region 940, the characteristic amplitudesof the digital transducer data are comparable in magnitude to thosemeasured from nearby force-imparting points that overlap force-measuringdevice 630A. The polarity of the digital transducer data forforce-imparting points in region 940 (second polarity, shown astriangles) is opposite to the polarity of the digital transducer datafor force-imparting points that overlap force-measuring device 630A(first polarity, shown as circles).

Suppose that we wish to construct a multi-virtual button user-inputsystem in which each force-measuring device corresponds to a respectivevirtual button. If the user-input system relies solely on thecharacteristic amplitudes of the digital transducer data, forcesimparted in region 940 can cause false-triggers. In this case, it mightnot be possible to distinguish user-inputs at force-measuring device630A from false-triggers in region 940. Based on the mapping resultsshown in plot 950, some of the aforementioned mechanical characteristicscan be modified to modify force-transmission from region 940 toforce-measuring device 630A. Additionally, or alternatively, theuser-input system can be configured to distinguish user-inputs based onthe characteristic amplitude and polarity of the digital transducerdata.

Plot 950 shows an oval region 930A surrounding the force-measuringdevice 630A. This oval region 930A approximately indicates a sensitivityregion in which a user-input intended for force-measuring device 630Acan be distinguished from a false-trigger input, when the false-triggerinput arises from an applied force imparted at a force-imparting pointremote from the force-measuring device 630A. For example, digitaltransducer data for force-imparting points in sensitivity region 930Ahave a first polarity and a characteristic amplitudes that are quitelarge (e.g., exceeding a predetermined threshold). Plot 950 also showssensitivity regions 930B and 930C surrounding force-measuring devices630B and 630C respectively. Forces imparted in sensitivity regions 930Band 930C are of an opposite polarity (second polarity) and hence can bedistinguished as false-triggers different from user-input in sensitivityregion 930A.

An area of sensitivity region 930A is several times larger than the areaof the force-measuring device 630A. Specifically, the force-measuringdevice 630A has lateral dimensions of 2.6 mm (along X-axis 982) by 1.4mm (along Y-axis 984). Accordingly, the force-measuring device 630Acovers an area of 3.64 mm². Oval region 930A has approximate dimensionsof 5.9 mm (along X-axis 982) by 5.0 mm (along Y-axis 984). This area isapproximately 23.2 mm², which is about 6.4 times greater than theforce-measuring device area. When implementing a virtual-button using aforce-measuring device, a sensitivity area that is at least three timesgreater, four times greater, five times greater, or six times greaterthan a lateral area of the force-measuring device can be achieved.

In plot 960, user-input in middle sensitivity region 930B, intended forforce-measuring device 630B, can be distinguished. For example, digitaltransducer data for force-imparting points in sensitivity region 930Bhave a first polarity and a characteristic amplitude that are quitelarge (e.g., exceed a predetermined threshold). Digital transducer datafor force-imparting points in right sensitivity region 930A havecharacteristic amplitudes that are quite small (e.g., less than apredetermined threshold) and digital transducer data for force-impartingpoints in left sensitivity region 930C have a second polarity oppositethe first polarity. The digital transducer data are of the firstpolarity in sensitivity regions 930A and 930B.

In plot 970, user-input in left sensitivity region 930C, intended forforce-measuring device 630C, can be distinguished. For example, digitaltransducer data for force-imparting points in sensitivity region 930Chave a first polarity and a characteristic amplitudes that are quitelarge (e.g., exceed a predetermined threshold). Digital transducer datafor force-imparting points in right sensitivity region 930A and middlesensitivity region 930B have characteristic amplitudes that are quitesmall (e.g., less than a predetermined threshold). The digitaltransducer data are of the first polarity in all three sensitivityregions 930A, 930B, and 930C.

Details and possible variations of the force-measuring device (630) arediscussed hereinbelow. FIG. 1 is a schematic view of an input system100. In the example shown, the input system 100 includes force-measuringdevices (102, 106) that are implemented as packaged integrated circuits(ICs) additionally including touch-sensing functionality. Such devicesare sometimes referred to as force-measuring and touch-sensingintegrated circuits (FMTSICs). Each of the force-measuring devices 102,106 has an electrical interconnection surface (bottom surface) 101, 105and an ultrasound transmission surface (top surface) 103, 107. TheFMTSICs 102, 106 are mounted to a flexible circuit substrate (flexiblecircuit) 108 (e.g., an FPC or flexible printed circuit) on theelectrical interconnection surfaces 101, 105. The flexible circuitsubstrate 108 is electrically and mechanically connected to a printedcircuit board (PCB) 112 via a connector 116. Other ICs 114 are mountedon the PCB 112, and such other ICs 114 could be a microcontroller (MCU),microprocessor (MPU), and/or a digital signal processor (DSP), forexample. These other ICs 114 could be used to run programs andalgorithms to analyze and categorize touch events based on data receivedfrom the FMTSICs 102, 106. Other ICs 114 can also be mounted to theflexible circuit. Generally, signal processing circuitry can beimplemented in the force-measuring devices (102, 106) and/or the ICs114. The signal processing circuitry can be implemented in a single IC,or in multiple ICs.

Input system 100 includes a cover layer 120 having an exposed outersurface 124 and an inner surface 122. The cover layer 120 could be ofany robust layer(s) that is sufficiently deformable such that adeformation of the cover layer is transmitted to the PMFEs in theFMTSICs, as described with reference to FIG. 5. In the case that theforce-measuring device 102, 106 includes ultrasonic transducers, thecover layer can be a material that transmits ultrasound waves. Examplesof robust materials that transmit ultrasound waves are wood, glass,metal, plastic, leather, fabric, and ceramic. The cover layer 120 couldalso be a composite stack of any of the foregoing materials. Theforce-measuring devices 102,106 are adhered to or attached to the innersurface 122 of the cover layer 120 by a layer of adhesive 110. Thechoice of adhesive 110 is not particularly limited as long as theforce-measuring devices 102, 106 remain attached to the cover layer. Theadhesive 110 could be double-sided tape, pressure sensitive adhesive(PSA), epoxy adhesive, or acrylic adhesive, for example. Force-measuringdevices 102, 106 are coupled to the inner surface 122. In someembodiments, the force-measuring device includes ultrasonic transducers.Ultrasonic transducers that can be fabricated usingmicro-electromechanical systems (MEMS) technologies includepiezoelectric micromechanical ultrasonic transducers (PMUTs) andcapacitive micromechanical ultrasonic transducers (CMUTs). In operation,ultrasonic transducers in the FMTSICs 102, 106 generate ultrasoundwaves. At least some of the generated ultrasound waves exit the FMTSICs102, 106 through the respective ultrasound transmission surfaces (topsurfaces) 103, 107, through the adhesive layer 110, then through theinner surface 122, and then through the cover layer 120. The ultrasoundwaves reach a sense region 126 of the exposed outer surface 124. Thesense region 126 is a region of the exposed outer surface 124 thatoverlaps the FMTSICs 102, 106. A MEMS chip that incorporates apiezoelectric micromechanical force-measuring element (PMFE) and apiezoelectric micromechanical ultrasound transducers (PMUT) is anexample of a FMTSIC, a force-measuring integrated circuit device thatadditionally incorporates touch-sensing functionality.

FIG. 1 illustrates a use case in which a human finger 118 is touchingthe cover layer at the sense region 126. If there is no object touchingthe sense region 126, the ultrasound waves that have propagated throughthe cover layer 120 are reflected at the exposed outer surface (at theair-material interface) and the remaining echo ultrasound waves travelback toward the FMTSICs 102, 106. On the other hand, if there is afinger 118 touching the sense region, there is relatively largeattenuation of the ultrasound waves by absorption through the finger. Asa result, it is possible to detect a touch event by measuring therelative intensity or energy of the echo ultrasound waves that reach theFMTSICs 102, 106.

It is possible to distinguish between a finger touching the sense region126 and a water droplet landing on the sense region 126, for example.When a finger touches the sense region 126, the finger would also exerta force on the cover layer 120. The force exerted by the finger on thecover layer can be detected and measured using the PMFEs in the FMTSIC.On the other hand, when a water droplet lands on the sense region, theforce exerted by the water droplet on the PMFEs would be quite small,and likely less than a noise threshold. More generally, it is possibleto distinguish between a digit that touches and presses the sense region126 and an inanimate object that comes into contact with the senseregion 126. In both cases (finger touching the sense region or waterdroplet landing on the sense region), there would be a noticeabledecrease in an amplitude of the PMUT receiver signal, indicating a touchat the sense region, but there might not be enough information from thePMUT receiver signal to distinguish between a finger and a waterdroplet.

FIG. 1 shows a finger-touch zone 119, which is a zone of contact betweenthe finger 118 and the cover layer 120. Finger-touch zone 119 has a size(a lateral dimension) that depends on factors such as size of the finger118 and whether the finger is a bare finger or a glove-covered finger.Typically, a finger-touch zone 119 can have a size in a range of 3 mm to7 mm. In the example shown, FMTSICs 102 and 106 are separated from eachother by a distance smaller than the finger-touch zone 119. Accordingly,FMTSICs 102 and 106 can correspond to a single virtual button. Atouch-input system can have multiple virtual buttons, and the virtualbuttons can be separated from each other by a distance greater than afinger-touch zone.

System 100 can be implemented in numerous apparatuses. For example, theFMTSICs can replace conventional buttons on Smartphones, keys oncomputer keyboards, sliders, or track pads. The interior contents 128 ofan apparatus (e.g., FMTSICs 102, 106, flexible circuit 108, connector116, PCB 112, other ICs 114) can be sealed off from the exterior 123 ofthe cover layer 120, so that liquids on the exterior 123 cannotpenetrate into the interior 121 of the apparatus. The ability to sealthe interior of an apparatus from the outside helps to make theapparatus, such as a Smartphone or laptop computer, waterproof. Thereare some applications, such as medical applications, where waterproofbuttons and keyboards are strongly desired. The apparatus can be amobile appliance (e.g., Smartphone, tablet computer, laptop computer), ahousehold appliance (e.g., washing machine, dryer, light switches, airconditioner, refrigerator, oven, remote controller devices), a medicalappliance, an industrial appliance, an office appliance, an automobile,or an airplane, for example.

The force-measuring, touch-sensing integrated circuit (FMTSIC) is shownin greater detail in FIG. 2. FIG. 2 is a cross-sectional view theforce-measuring device (more specifically, FMTSIC) 20, which isanalogous to FMTSIC 102, 106 in FIG. 1. FMTSIC 20 is shown encased in apackage 22, with an ultrasound transmission surface (top surface) 26 andelectrical interconnection surface (bottom surface) 24. Ultrasoundtransmission surface 26 is analogous to surfaces 103, 107 in FIG. 1 andelectrical interconnection surface 24 is analogous to surfaces 101, 105in FIG. 1. The FMTSIC 20 includes a package substrate 30, semiconductorportion (chip) 28 mounted to the package substrate 30, and anencapsulating adhesive 32, such as an epoxy adhesive. After thesemiconductor die 28 is mounted to the package substrate 30, wire bondconnections 38 are formed between the die 28 and the package substrate30. Then the entire assembly including the die 28 and the packagesubstrate 30 are molded (encapsulated) in an epoxy adhesive 32. Theepoxy side (top surface or ultrasound transmission surface 26) of theFMTSIC is adhered to (coupled to) the inner surface 122 of the coverlayer 120. The FMTSIC 20 is shown mounted to the flexible circuit 108.It is preferable that the FMTSIC have lateral dimensions no greater than10 mm by 10 mm. The wire bond connection is formed between the topsurface 36 of the semiconductor die 28 and the package substrate 30.Alternatively, electrical interconnections can be formed between thebottom surface 34 of the semiconductor die 28 and the package substrate.The semiconductor die 28 consists of an application-specific integratedcircuit (ASIC) portion and a micro-electro-mechanical systems (MEMS)portion. A selected portion 130 of the semiconductor die 28 is shown incross-section in FIG. 3.

FIG. 3 is a schematic cross-sectional view of a portion 130 of theforce-measuring and touch-sensing integrated circuit of FIG. 2. Thesemiconductor die 28 includes a MEMS portion 134 and an ASIC portion136. Between the ASIC portion 136 and the MEMS portion 134, the MEMSportion 134 is closer to the ultrasound transmission surface 26 and theASIC portion 136 is closer to the electrical interconnection surface 24.The ASIC portion 136 consists of a semiconductor substrate 150 andsignal processing circuitry 137 thereon. Typically, the semiconductorsubstrate is a silicon substrate, but other semiconductor substratessuch as silicon-on-insulator (SOI) substrates can also be used.

The MEMS portion 134 includes a PMUT transmitter 142, a PMUT receiver144, and a PMFE 146. The MEMS portion 134 includes a thin-filmpiezoelectric stack 162 overlying the semiconductor substrate 150. Thethin-film piezoelectric stack 162 includes a piezoelectric layer 160,which is a layer exhibiting the piezoelectric effect. Suitable materialsfor the piezoelectric layer 160 are aluminum nitride, scandium-dopedaluminum nitride, polyvinylidene fluoride (PVDF), lead zirconatetitanate (PZT), K_(x)Na_(1-x)NbO₃ (KNN), quartz, zinc oxide, and lithiumniobate, for example. For example, the piezoelectric layer is a layer ofaluminum nitride having a thickness of approximately 1 μm. Thepiezoelectric layer 160 has a top major surface 166 and a bottom majorsurface 164 opposite the top major surface 166. In the example shown,the thin-film piezoelectric stack 162 additionally includes a topmechanical layer 156, attached to or adjacent to (coupled to) top majorsurface 166, and a bottom mechanical layer 154, attached to or adjacentto (coupled to) bottom major surface 164. In the example shown, thethickness of the top mechanical layer 156 is greater than the thicknessof the bottom mechanical layer 154. In other examples, the thickness ofthe top mechanical layer 156 can be smaller than the thickness of thebottom mechanical layer 154. Suitable materials for the mechanicallayer(s) are silicon, silicon oxide, silicon nitride, and aluminumnitride, for example. Suitable materials for the mechanical layer(s) canalso be a material that is included in the piezoelectric layer 160,which in this case is aluminum nitride. In the example shown, the topmechanical layer and the bottom mechanical layer contain the samematerial. In other examples, the top mechanical layer and the bottommechanical layer are of different materials. In other examples, one ofthe top mechanical layer and the bottom mechanical layer can be omitted.The mechanical layer(s) adjust the mechanical properties of thethin-film piezoelectric stack 162. When coupled to the cover layer, theFMTSIC 20 is preferably oriented such that the piezoelectric layer 160faces toward the cover layer 120. For example, the FMTSIC 20 is orientedsuch that the piezoelectric layer 160 and the cover layer 120 areapproximately parallel.

For ease of discussion, only one of each of the PMUT transmitters, PMUTreceivers, and PMFEs is shown in FIG. 3. However, a typical FMTSIC cancontain a plurality of PMUT transmitters, PMUT receivers, and PMFEs. ThePMUT transmitters, the PMUT receivers, and the PMFEs are located alongrespective lateral positions along the thin-film piezoelectric stack162. Each PMUT transmitter, PMUT receiver, and PMFE includes arespective portion of the thin-film piezoelectric stack. In aforce-measuring device that does not have touch-sensing functionality,the PMUT transmitters and PMUT receivers can be omitted. An insulatingsupport layer 152 supports the thin-film piezoelectric stack. Suitablematerials for the support layer 152 are silicon, silicon nitride, andsilicon oxide, for example. Suitable materials for the support layer 152can also be a material that is included in the piezoelectric layer 160,which in this case is aluminum nitride.

Each PMFE 146 includes a respective portion of the thin-filmpiezoelectric stack 162. Each PMFE 146 includes a first PMFE electrode176 positioned on a first side (bottom surface) 164 of the piezoelectriclayer 160 and a second PMFE electrode 186 positioned on a second side(top surface) 166 opposite the first side. The first PMFE electrode 176and the second PMFE electrode 186 are positioned on opposite sides ofthe piezoelectric layer 160. In each PMFE 146, the first PMFE electrode176, the second PMFE electrode 186, and the portion of the piezoelectriclayer 160 between them constitute a piezoelectric capacitor. The PMFEsare coupled to the signal processing circuitry 137 as explained indetail hereinbelow.

A portion 132 of the FMTSIC 20 containing a PMFE 146 is shown in crosssection in FIG. 4. Also shown is the ASIC portion 136 that is under thePMFE 146 and the encapsulating adhesive 32 that is above the PMFE 146.FIG. 10 shows the PMFE in a quiescent state, in which there is noflexing of the piezoelectric stack 162. In the quiescent state, there isno voltage generated between the PMFE electrodes (176, 186).

FIGS. 5, 6, and 7 are schematic side views of an FMTSIC 20 and a coverlayer 120 attached to or adhered to (coupled to) each other. A topsurface (ultrasound transmission surface) 26 of FMTSIC 20 is coupled toinner surface 122 of the cover layer 120. FMTSIC 20 and cover layer 120overlie a rigid substrate 135. For ease of viewing, other components ofsystem 100 (e.g., flexible circuit 108, ICs 114) have been omitted.FMTSIC 20 includes PMFEs 146. In the examples shown, two anchor posts131, 133 fix the two ends of the cover layer 120 to the substrate 135.

In the example of FIG. 5, FMTSIC 20 is not anchored to the rigidsubstrate 135 and can move with the cover layer 120 when the cover layer120 is deflected upwards or downwards. A downward force 117, shown as adownward arrow, is applied by a finger (or another object) pressingagainst the outer surface 124 of the cover layer 120 at the sense region126 for example. A finger pressing against or tapping the outer surface124 are examples of touch excitation, or more generally, excitation. Inthe example shown in FIG. 5, the cover layer 120 is deflected in a firstdirection (e.g., downwards) in response to a touch excitation at thesense region 126. FMTSIC 20 is located approximately half-way betweenthe anchor posts 131, 133 and sense region 126 overlaps FMTSIC 20. Aneutral axis 125 is located within the cover layer 120. A lower portion127 of the cover layer 120, below the neutral axis 125, is under tensile(positive) strain at the sense region 126, represented by outwardpointing arrows, primarily along lateral direction 191, perpendicular tothe normal direction 190. Normal direction 190 is normal to thepiezoelectric layer 160. Normal direction 190 is approximately normal toa plane of the respective piezoelectric capacitor. The piezoelectriclayer 160 has a built-in polarization (piezoelectric polarization) thatis approximately parallel to normal direction 190. The lateral direction191 is approximately parallel to the piezoelectric layer 160 at therespective location of the piezoelectric layer 160 (at region 126). Anupper portion 129 of the cover layer 120, above the neutral axis 125, isunder compressive (negative) strain at the sense region 126, representedby inward pointing arrows, primarily along lateral direction 191. SinceFMTSIC 20 is coupled to the inner surface 122, adjacent to the lowerportion 127, the PMFEs 146 are also under tensile (positive) strain.Typically, the entire FMTSIC 20 may be deflected under the applieddownward force 117. In the example shown in FIG. 5, the PMFEs 146 areunder a positive strain, and the respective portions of thepiezoelectric layer 160 at the PMFEs 146 undergo expansion along alateral direction 191. As a result, an electrical charge is generated ateach PMFE (146) between the respective PMFE electrodes (176, 186). Thiselectrical charge is detectable as a first deflection voltage V_(d1)(corresponding to strain of a certain polarity and magnitude). Thepolarity of the first deflection voltage V_(d1) at a PMFE depends uponthe polarity of the strain (positive strain (tensile) or negative strain(compressive)) at the respective portion of the piezoelectric layerbetween the respective PMFE electrodes of the PMFE. The magnitude of thefirst deflection voltage V_(d1) at a PMFE depends upon the magnitude ofthe strain at the respective portion of the piezoelectric layer betweenthe respective PMFE electrodes of the PMFE. Subsequently, when thedownward force 117 is no longer applied to the sense region 126, thecover layer 120 deflects in a second direction opposite the firstdirection (e.g., upwards). This is detectable as a second deflectionvoltage V_(d2) (corresponding to strain of a certain polarity andmagnitude). The polarity of the second deflection voltage V_(d2) at aPMFE depends upon the polarity of the strain at the respective portionof the piezoelectric layer between the respective PMFE electrodes of thePMFE. The magnitude of the second deflection voltage V_(d2) at a PMFEdepends upon the magnitude of the strain at the respective portion ofthe piezoelectric layer between the respective PMFE electrodes of thePMFE.

FIG. 5 shows a second FMTSIC 20A, including PMFEs 146A. A top surface(ultrasound transmission surface) 26A of FMTSIC 20A is coupled to innersurface 122 of the cover layer 120. FMTSIC 20A overlies the rigidsubstrate 135 and is located at a second region 126A, between anchorpost 131 and first FMTSIC 20. Note that FMTSIC 20A is laterallydisplaced from the location where the downward force 117 is applied tothe outer surface 124 (at sense region 126). The lower portion 127 ofthe cover layer 120 is under compressive (negative) strain at the secondregion 126A, represented by inward pointing arrows, primarily along thelateral direction 191A, perpendicular to the normal direction 190A. Thelateral direction 191A is approximately parallel to the piezoelectriclayer 160 at the respective location of the piezoelectric layer 160 (atsecond region 126A). The upper portion 129 of the cover layer 120 isunder tensile (positive) strain at the second region 126A, representedby outward pointing arrows, primarily along the lateral direction 191A.Since FMTSIC 20A is coupled to the inner surface 122, adjacent to thelower portion 127, the PMFEs 146A are also under compressive (negative)strain. These examples illustrate that when the cover layer and theFMTSICs undergo deflection in response to a touch excitation at theouter surface, expansion and/or compression of the piezoelectric layeralong the lateral direction may be induced by the deflection of thecover layer.

In the example shown in FIG. 6, the bottom surface 24 of FMTSIC 20 isanchored to the rigid substrate 135. When downward force 117 is appliedto the outer surface 124 of the cover layer 120 at sense region 126, theportion of the cover layer 120 at the sense region 126 transmits thedownward force along normal direction 190. The portion of the coverlayer 120 at the sense region 126 and the FMTSIC 20 undergo compressionalong normal direction 190. Consequently, the PMFEs 146 includingpiezoelectric layer 160 are compressed along the normal direction 190,approximately normal to the piezoelectric layer 160. As a result, anelectrical charge is generated between the PMFE electrodes (176, 186).This electrical charge is detectable as a voltage V_(c) (correspondingto a strain of a certain polarity and magnitude) between the PMFEelectrodes. The downward force 117 that causes this compression isapplied during a touch excitation, such as tapping at or pressingagainst the outer surface 124. The pressing or the tapping can berepetitive. Typically, the entire FMTSIC 20 may undergo compression.Subsequently, the piezoelectric layer 160 relaxes from the compressedstate. In other cases, there may also be compression along a lateraldirection 191, or along other directions.

In the example shown in FIG. 7, FMTSIC 20 is not anchored to the rigidsubstrate 135. A downward force 139, shown as a downward arrow, isapplied to the outer surface 124 of the cover layer 120 at the senseregion 126. The downward force 139 is generated as a result of an impactof touch excitation at the sense region 126. For example, the downwardforce 139 is generated as a result of the impact of a finger (or anotherobject) tapping the outer surface at the sense region 126. The touchexcitation (e.g., tapping) can be repetitive. The impact of the touchexcitation (e.g., tapping) generates elastic waves that travel outwardfrom the location of the impact (on the outer surface 124 at senseregion 126) and at least some of the elastic waves travel toward theinner surface 122. Accordingly, at least some portion 149 of the elasticwaves are incident on the FMTSIC 20.

In general, an impact of a touch excitation (e.g., tapping) on a surfaceof a stack (e.g., cover layer) can generate different types of wavesincluding pressure waves, shear waves, surface waves and Lamb waves.Pressure waves, shear waves, and surface waves are in a class of wavescalled elastic waves. Pressure waves (also called primary waves orP-waves) are waves in which the molecular oscillations (particleoscillations) are parallel to the direction of propagation of the waves.Shear waves (also called secondary waves or S-waves) are waves in whichthe molecular oscillations (particle oscillations) are perpendicular tothe direction of propagation of the waves. Pressure waves and shearwaves travel radially outwards from the location of impact. Surfacewaves are waves in which the energy of the waves are trapped within ashort depth from the surface and the waves propagate along the surfaceof the stack. Lamb waves are elastic waves that can propagate in plates.When an object (e.g., a finger) impacts a surface of a stack, differenttypes of elastic waves can be generated depending upon the specifics ofthe impact (e.g., speed, angle, duration of contact, details of thecontact surface), the relevant material properties (e.g., materialproperties of the object and the stack), and boundary conditions. Forexample, pressure waves can be generated when an impact of a touchexcitation at the outer surface is approximately normal to the outersurface. For example, shear waves can be generated when an impact of atouch excitation at the outer surface has a component parallel to theouter surface, such as a finger hitting the outer surface at an obliqueangle or a finger rubbing against the outer surface. Some of theseelastic waves can propagate towards the FMTSIC 20 and PMFEs 146. If thestack is sufficiently thin, then some portion of surface waves canpropagate towards the FMTSIC 20 and PMFEs 146 and be detected by thePMFEs 146.

Accordingly, when elastic waves 149 are incident on the FMTSIC 20 andPMFEs 146, the elastic waves induce time-dependent oscillatorydeformation to the piezoelectric layer 160 at the PMFE 146. Thisoscillatory deformation can include: lateral deformation (compressionand expansion along the lateral direction 191 approximately parallel topiezoelectric layer 160), normal deformation (compression and expansionalong the normal direction 190 approximately normal to the piezoelectriclayer 160), and shear deformation. As a result, time-varying electricalcharges are generated at each PMFE (146) between the respective PMFEelectrodes (176, 186). These time-varying electrical charges aredetectable as time-varying voltage signals. The signal processingcircuitry amplifies and processes these time-varying voltage signals.Typically, the time-dependent oscillatory deformations induced by animpact of a touch excitation are in a frequency range of 10 Hz to 1 MHz.For example, suppose that elastic waves 149 include pressure wavesincident on the PMFEs 146 along the normal direction 190; these pressurewaves may induce compression (under a positive pressure wave) andexpansion (under a negative pressure wave) of the piezoelectric layer160 along the normal direction 190. As another example, suppose thatelastic waves 149 include shear waves incident on the PMFEs 146 alongthe normal direction 190; these shear waves may induce compression andexpansion of the piezoelectric layer 160 along the lateral direction191.

Consider another case in which a downward force 139A, shown as adownward arrow, is applied to the outer surface 124 at a second region126A, between anchor post 131 and FMTSIC 20. The downward force 139A isgenerated as a result of an impact of touch excitation at the secondregion 126A. The impact of the touch excitation generates elastic wavesthat travel outward from the location of the impact (region 126A) and atleast some of the elastic waves travel towards the inner surface 122.Accordingly, at least some portion 149A of the elastic waves areincident on the FMTSIC 20, causing the piezoelectric layer 160 toundergo time-dependent oscillatory deformation. As a result,time-varying electrical charges are generated at each PMFE (146) betweenthe respective PMFE electrodes (176, 186). These time-varying electricalcharges are detectable as time-varying voltage signals, although theimpact of the touch excitation occurred at a second region 126A that islaterally displaced from the sense region 126.

Elastic waves 149A that reach FMTSIC 20 from region 126A may be weaker(for example, smaller in amplitude) than elastic waves 149 that reachFMTSIC 20 from sense region 126, because of a greater distance betweenthe location of impact and the FMTSIC. An array of PMFEs can beconfigured to be a position-sensitive input device, sensitive to alocation of the impact (e.g., tapping) of a touch excitation. An arrayof PMFEs can be an array of PMFEs in a single FMTSIC or arrays of PMFEsin multiple FMTSICs. For example, a table input apparatus could have anarray of FMTSICs located at respective lateral positions underneath thetable's top surface, in which each FMTSIC would contain at least onePMFE and preferably multiple PMFEs. The signal processing circuitry canbe configured to amplify and process the time-varying voltage signalsfrom the PMFEs and analyze some features of those time-varying voltagesignals. Examples of features of time-varying voltage signals are: (1)amplitudes of the time-varying voltage signals, and (2) the relativetiming of time-varying voltage signals (the “time-of-flight”). Forexample, a PMFE exhibiting a shorter time-of-flight is closer to thelocation of impact than another PMFE exhibiting a longer time-of-flight.The signal processing circuitry can analyze features of time-varyingsignals (e.g., amplitude and/or time-of-flight) from the PMFEs in anarray of PMFEs to estimate a location of impact of a touch excitation.

In operation, PMFE 146 is configured to output voltage signals betweenthe PMFE electrodes (176, 186) in accordance with a time-varying strainat the respective portion of the piezoelectric layer between the PMFEelectrodes (176, 186) resulting from a low-frequency mechanicaldeformation. A touch excitation at the cover layer or at anothercomponent mechanically coupled to the cover layer causes a low-frequencymechanical deformation (of the cover layer or other component at thepoint of excitation). The touch excitation induces effects includingdeflection (as illustrated in FIG. 5), compression (as illustrated inFIG. 6), and/or elastic-wave oscillations (as illustrated in FIG. 7). Inan actual touch event, more than one of these effects may be observable.Consider tapping by a finger as an example of a touch excitation. As thefinger impacts the outer surface 124, elastic waves are generated whichare detectable as time-varying voltage signals at the PMFEs (FIG. 7).Elastic waves are generated by the impact of the touch excitation.Subsequently, as the finger presses against the cover layer, the FMTSICundergoes deflection (FIG. 5). There is expansion or compression of thepiezoelectric layer along a lateral direction. The low-frequencymechanical deformation can be caused by a finger pressing against ortapping at outer surface of the cover layer 120, to which the FMTSIC 20is attached (coupled). The PMFE 146 is coupled to the signal processingcircuitry 137. By amplifying and processing the voltage signals from thePMFE at the signal processing circuitry, the strain that results fromthe mechanical deformation of the piezoelectric layer can be measured.

It is possible to adjust the relative amplitudes of the PMFE voltagesignals attributable to the elastic-wave oscillations (FIG. 7) andlateral expansion and compression due to deflection (FIG. 5). Forexample, one can choose the cover layer to be more or less deformable.For example, the cover layer 120 of FIG. 7 may be thicker and/or made ofmore rigid material than the cover layer 120 of FIG. 5.

PMFE 146 is configured to output voltage signals between the PMFEelectrodes (176, 186) in accordance with a time-varying strain at therespective portion of the piezoelectric layer between the PMFEelectrodes (176, 186) resulting from a low-frequency mechanicaldeformation. Typically, the low-frequency deformation is induced bytouch excitation which is not repetitive (repetition rate is effectively0 Hz) or is repetitive having a repetition rate of 100 Hz or less, or 10Hz or less. These repetition rates correspond to the repetition rates ofa repetitive touch excitation, e.g., a finger repeatedly pressingagainst or tapping the sense region.

A touch excitation, or more generally, excitation can occur somewhereother than at the sense region. Consider an implementation of FMTSICs ina portable apparatus, such as a smartphone. In some cases, the coverlayer, to which the FMTSIC is coupled, can be a portion of thesmartphone housing, and in other cases, the housing and the cover layercan be attached to each other, such that forces applied to the housingcan be transmitted to the cover layer. We can refer to both cases as acomponent (e.g., housing) being mechanically coupled to the cover layer.Excitation such as bending of, twisting of, pinching of, typing at, andtapping at the housing can also cause low-frequency mechanicaldeformation. For example, typing at the housing can include typing at atouch panel of the smartphone. There can be a time-varying strain(force) at a respective portion of the piezoelectric layer at a PMFEresulting from this low-frequency deformation.

A force-measuring device may contain multiple PMFEs. FIG. 8 is a topview of an example MEMS portion 200 of a force-measuring device 198. TheMEMS portion includes four PMFEs (214, locations identified as p, q, r,and s) arranged in a two-dimensional array 212 extending along theX-axis (220) and Y-axis (222). The PMFEs are arranged in columns (A andB) and rows (1 and 2). In the example shown, the two-dimensional PMFEarray 212 has a square outer perimeter, but in other examples the outerperimeter can have other shapes such as a rectangle. Each PMFE issensitive to a mechanical deformation (measurable as a strain) at itsrespective X and Y location, resulting from a particular applied force(e.g., touch excitation). In this sense, the PMFE array 212 achieves atwo-dimensional positional resolution of measurement of the appliedforce.

An FMTSIC can contain multiple PMUT transmitters, PMUT receivers, andPMFEs. FIG. 9 is a top view of a MEMS portion 250 of an FMTSIC 20. ThePMUTs (PMUT transmitters 204 shown as white circles and PMUT receivers206 shown as grey circles) are arranged in a two-dimensional array,extending along the X-axis (220) and Y-axis (222). The PMUTs arearranged in columns (A, B, C, and D) and rows (1, 2, 3, and 4).

The MEMS portion 250 includes eight PMFEs (254) arranged in atwo-dimensional array 252. The PMFE array 252 has an opening, which isdevoid of PMFEs, in which the PMUT array 202 is disposed. The PMFEs arearranged into four sets (260, 262, 264, and 266), where each set isassociated with a different X and Y location. Therefore, the PMFE array252 achieves a two-dimensional positional resolution of applied forcesmeasurement. The PMFE array enables calculation of force-resolutionfeatures, discussed hereinbelow. Each PMFE set contains two PMFEs. Inthe example shown, set 260 contains t1 and t2, set 262 contains u1 andu2, set 264 contains v1 and v2, and set 266 contains w1 and w2. ThePMFEs in a set are electrically connected to each other. In thisexample, the piezoelectric capacitors constituting each PMFE in a setare connected to each other in series. An advantage to combining thetouch-sensing (PMUTs) and force-measuring (PMFEs) functions into oneintegrated circuit device is that it becomes possible to distinguishbetween stationary objects that touch but do not apply significant force(e.g., water droplet on sense region 126) and moving objects that touchand apply significant force (e.g., finger).

FIG. 10 is a cross-sectional view of a force-measuring device 270.Force-measuring device 270 is an alternative to force-measuring device20 (FIG. 2). Force-measuring device 270 is shown encased in a package22, with an ultrasound transmission surface (top surface) 26 andelectrical interconnection surface (bottom surface) 24. In the exampleshown, the force-measuring device 270 is an IC and can be implemented asan FMTSIC. The force-measuring device 270 includes a package substrate30, semiconductor die (semiconductor chip) 28 mounted to the packagesubstrate 30, a MEMS chip 40 on the semiconductor die 28, and anencapsulating adhesive 32, such as an epoxy adhesive. Force-measuringdevice 270 differs from force measuring device 20 (FIG. 2) in that itadditionally includes a MEMS chip 40. The MEMS chip 40 and thesemiconductor chip 28 are shown bonded together in a bonded chipassembly 42. This is an example of the semiconductor substrate and theMEMS substrate being attached to each other at their major surfaces. Aselected portion 272 of the bonded chip assembly 42 is shown incross-section in FIG. 11.

FIG. 11 is a schematic cross-sectional view of a portion 272 of theforce-measuring device 270 of FIG. 10. The semiconductor die 28 includesan ASIC portion 136 and the MEMS chip includes a MEMS portion 134. TheASIC portion 136 consists of a semiconductor substrate 150 and signalprocessing circuitry 137 thereon. Typically, the semiconductor substrateis a silicon substrate, but other semiconductor substrates such assilicon-on-insulator (SOI) substrates can also be used. The MEMS portion134 includes a MEMS substrate 276 and MEMS structures disposed on theMEMS substrate 276. Suitable MEMS substrates include silicon and glass.MEMS structures shown in FIG. 11 include the piezoelectric stack 162(piezoelectric layer 160, bottom mechanical layer 154, top mechanicallayer 156), a first PMFE electrode 176, and a second PMFE electrode 186.A wafer bond layer 274, located between the ASIC portion 136 and theMEMS portion 134, bonds the two portions together.

A bonded assembly including a MEMS portion and an ASIC portion can beformed as follows. MEMS structures are formed on a MEMS substrate, andsignal processing circuitry is formed on a semiconductor substrate.Subsequently, the MEMS substrate and the semiconductor substrate arebonded together by a wafer-bonding process, resulting in a wafer bondlayer (274) between the substrates. The resulting MEMSsubstrate-semiconductor substrate assembly is singulated to form aplurality of bonded chip assemblies 42 including a MEMS portion 40 andan ASIC portion 28. After the bonded chip assembly 42 is mounted to thepackage substrate 30, wire bond connections 38 are formed between thebonded chip assembly 42 and the package substrate 30. Then the entireassembly including the bonded chip assembly 42 and the package substrate30 are molded (encapsulated) in an epoxy adhesive 32. Additionalexplanation is provided with reference to FIG. 18 hereinbelow.

FIG. 12 is a cross-sectional view of a MEMS device 280. Unlike theforce-measuring devices 20 (FIGS. 2) and 270 (FIG. 10), MEMS device 280itself is devoid of the signal processing circuitry necessary foroperation of the PMFEs. However, when connected to the necessary signalprocessing circuitry, MEMS device 280 can be configured to operate as aforce-measuring device. Referring to the example shown in FIG. 12, thissignal processing circuitry can be contained in ICs 114, for example.Hence, MEMS device 280 is sometimes referred to as a force-measuringdevice. MEMS device 280 is shown encased in a package 22, with anultrasound transmission surface or a top surface 26 and electricalinterconnection surface (bottom surface) 24. The MEMS device 280includes a package substrate 30, MEMS chip 40 mounted to the packagesubstrate 30, and an encapsulating adhesive 32, such as an epoxyadhesive. A selected portion 282 of the MEMS chip is shown incross-section in FIG. 13.

FIG. 13 is a schematic cross-sectional view of a portion 282 of the MEMSdevice 280 of FIG. 12. The MEMS chip 40 includes a MEMS portion 134. TheMEMS portion 134 includes a MEMS substrate 276 and MEMS structuresdisposed on the MEMS substrate 276. Suitable MEMS substrates includesilicon and glass. MEMS structures shown in FIG. 13 include thepiezoelectric stack 162 (piezoelectric layer 160, bottom mechanicallayer 154, top mechanical layer 156), a first PMFE electrode 176, and asecond PMFE electrode 186.

FIG. 14 is an electronics block diagram of the force-measuring device198, including a MEMS portion 200 (FIG. 8) and signal processingcircuitry 137. The MEMS portion includes PMFEs 214. The signalprocessing circuitry 137 includes amplifiers (402), analog-to-digitalconverters (ADCs) (406), and other circuit blocks (410). Voltage signalsread from PMFEs 214 reach amplifiers 402 via electrical interconnections404 and get amplified by the amplifiers 402. These amplified voltagesignals are sent to ADC 406 to be converted to digital signals which canbe processed or stored by other circuit blocks 410. The other circuitblocks 410 could be microcontrollers (MCUs), memories, and digitalsignal processors (DSPs), for example. Force-measuring device 198 isimplemented as a force-measuring device that does not have touch-sensingfunctionality (hence, not an FMTSIC). In the case of force-measuringdevice 270, the signal processing circuitry would be present in therespective device. On the other hand, when implementing aforce-measuring device using a MEMS device 280 (FIG. 12), the signalprocessing circuitry would be implemented somewhere outside of the MEMSdevice 280, such as in another IC 114 (FIG. 1).

FIG. 15 is an electronics block diagram of the FMTSIC 20, including aMEMS portion 134 and signal processing circuitry 137. The MEMS portionincludes PMUT transmitters 142, PMUT receivers 144, and PMFEs 146.Signal processing circuitry 137 includes a high-voltage domain 280 and alow-voltage domain 290. The high-voltage domain is capable of operatingat higher voltages required for driving the PMUT transmitters. Thehigh-voltage domain includes high-voltage transceiver circuitry 282,including high-voltage drivers. The high-voltage transceiver circuitry282 is connected to the first PMUT electrodes and the second PMUTelectrodes of the PMUT transmitters, via electrical interconnections(wiring) 284. The high-voltage transceiver is configured to outputvoltage pulses of 5 V or greater, depending on the requirements of thePMUT transmitters. The processing circuit blocks 288 are electricallyconnected to the high-voltage transceiver circuitry 282 and theanalog-to-digital converters (ADCs) (296, 306). The processing circuitblocks 288 generate time-varying signals that are transmitted to thehigh-voltage transceiver circuitry 282. The high-voltage transceivercircuitry 282 transmits high-voltage signals to the PMUT transmitters142 in accordance with the time-varying signals from the processingcircuit blocks 288.

The low-voltage domain 290 includes amplifiers (292, 302) andanalog-to-digital converters (ADCs) (296, 306). The processing circuitblocks 288 are also contained in the low-voltage domain 290. Voltagesignals output by the PMUT receivers 144 (represented by gray circles)reach amplifiers 302 via electrical interconnections (wiring) 304 andget amplified by the amplifiers 302. The amplified voltage signals aresent to ADC 306 to be converted to digital signals which can beprocessed or stored by processing circuit blocks 288. Similarly, voltagesignals output by PMFEs 146 reach amplifiers 292 via electricalinterconnections (wiring) 294 and get amplified by the amplifiers 292.These amplified voltage signals are sent to ADC 296 to be converted todigital signals which can be processed or stored by processing circuitblocks 288. The processing circuit blocks 288 could be microcontrollers(MCUs), memories, and digital signal processors (DSPs), for example. Thewiring (284, 294, 304) traverses the semiconductor substrate, whichcontains the signal processing circuitry 137, and the MEMS portion 134,which contains the PMFEs 146, the PMUT transmitters 142, and the PMUTreceivers 144.

In the example shown (FIG. 15), the piezoelectric capacitorsconstituting the PMUT receivers 144 are connected to each other inparallel. Since the capacitances of these PMUT receivers are addedtogether, this arrangement of PMUT receivers is less sensitive to theeffects of parasitic capacitance. Accordingly, there is a unifiedvoltage signal transmitted from the PMUT receivers 144 to the amplifiers302. The piezoelectric capacitors constituting the PMUT transmitters 142are connected in parallel. Accordingly, there is a time-varying signaltransmitted from the high-voltage transceiver circuitry 282 to the PMUTtransmitters 142. The PMFEs 146 are grouped into two sets (p and q onthe left side, r and s on the right side), and the PMFEs in each set areconnected to each other in series. Accordingly, there are two sets ofPMFE signals transmitted from the PMFEs 146 to the amplifiers 292.

The three implementations of the force-measuring device shown in FIGS.2, 10, and 12 employed piezoelectric micromechanical force-measuringelements. However, a force-measuring device need not be limited tomicromechanical elements and/or piezoelectric elements. For example, apiezoelectric capacitor comprising a non-micromechanical piezoelectricfilm and electrodes on opposite sides of the film or a piezoresistivestrain gauge can be used to carry out the force-measuring functionalityof a force-measuring device.

FIG. 16 is a schematic view of an input system 500 havingforce-measuring and touch-sensing capabilities (force-measuring andtouch-sensing system 500). System 500 is an example of an electronicapparatus that can undergo testing and calibration (FIG. 28) or fromwhich a mapping of force transmission from a plurality offorce-imparting points to each force-measuring device can be obtained(FIG. 31). The force-measuring and touch-sensing system 500 includes oneor more force-measuring devices 102 (five are shown) and a capacitivetouch panel assembly 520. In other examples, it is possible for a systemto have less than five or more than five force-measuring devices. In theexample shown in FIG. 16, each of the force-measuring devices 102 isshown in the form of a packaged chip. The force-measuring device chips102 are mounted to a flexible circuit substrate 108 (e.g., an FPC orflexible printed circuit). The flexible circuit substrate 108 iselectrically and mechanically connected to a printed circuit board (PCB)112 via a connector 116. Additionally, a touch panel controller 534 andother integrated circuits (other ICs) 514 are mounted on the PCB 112.Generally, signal processing circuitry can be implemented in theforce-measuring device 102, the touch panel controller 534, and/or theother ICs 114. The signal processing circuitry can be implemented in asingle IC, or in multiple ICs. Other ICs 114 can include amicrocontroller (MCU), microprocessor (MPU), and/or a digital signalprocessor (DSP), for example.

In the example shown, the capacitive touch panel assembly 520 isembedded in a cover layer 120. The touch panel assembly 520 has anexposed outer surface 524 and an inner surface 522. The force-measuringdevices 102 are adhered to the inner surface 522 of the touch panelassembly 520 by a layer of adhesive 110. The choice of adhesive 110 isnot particularly limited as long as the devices 102 remain attached tothe cover layer. The adhesive 110, the cover layer 120, theforce-measuring devices 102, and the flexible circuit substrate 108 havebeen discussed with reference to FIG. 1.

The capacitive touch panel assembly 520 includes a grid region 530containing wiring traces 540 extending in the X-direction (220) andwiring traces 542 extending in the Y-direction (into the page,perpendicular to the X-direction 220 and Z-direction 224). Thecapacitive touch panel assembly 520 is coupled to the touch panelcontroller IC 534 via a connector 532. For example, the touch panelcontroller 534 contains signal processing circuitry that measures thecapacitance at each intersection of the X-direction wiring traces 540and Y-direction wiring traces 542. For example, when a finger 118touches a region of the capacitive touch panel assembly 520, themeasured capacitance in the touched region changes Preferably, thecapacitive touch panel assembly also includes a display, such as adeformable OLED (organic light-emitting diode) display or a deformableliquid crystal display (LCD). Preferably, the capacitive touch panelassembly 520 is sufficiently deformable such that when a force isimparted to the touch panel assembly on the outer surface 524, theforce-measuring devices 102 that are adhered to the capacitive touchpanel assembly 520 at its inner surface 522 also undergo deformation.

FIG. 17 shows a flow diagram of a method 550 of making force-measuringdevice (20 of FIG. 2), making an electronic apparatus incorporating theforce-measuring device, and calibrating the force-measuring device ormapping data of force transmission to the force-measuring device. Atstep 552, the CMOS wafer is fabricated using a semiconductor substrate.The ASIC portion 136 including signal processing circuitry 137 isfabricated on a semiconductor substrate (wafer) 150 using a CMOSfabrication process. At step 554, the MEMS portion 134 is fabricated ontop of the ASIC portion 136. At step 556, the force-measuring devices(20) are made. This step 556 includes, for example, the singulation ofthe wafer into dies, the mounting of dies onto a package substrate, andthe packaging of the die including application of an epoxy adhesive. Atstep 556, the force-measuring devices (20) are optionally incorporatedinto an electronic apparatus (640). This may include: connectingforce-measuring devices to other components in the electronic apparatus;electronically coupling the force-measuring devices to other circuitelements in the electronic apparatus; and attaching the force-measuringdevices to an interior surface of an external housing of the electronicapparatus. For example, the electronic apparatus 640 can be a mobileappliance (e.g., Smartphone, tablet computer, laptop computer, display)or any other electronic apparatus, such as a user-interface subsystem ina mobile appliance, a household appliance (e.g., washing machine, drier,light switches, air conditioner, refrigerator, oven, remote controllerdevices), a medical appliance, an industrial appliance, an officeappliance, an automobile, or an airplane. At step 558, theforce-measuring device undergoes calibration, either in its standalonestate or after incorporation into an electronic apparatus, according tomethod 800 (FIG. 28) or a mapping of data of force transmission from aplurality of force-imparting points to the force-measurement device isobtained according to method 870 (FIG. 31).

FIG. 18 shows a flow diagram of a method 560 of making force-measuringdevice (270 of FIG. 10), making an electronic apparatus incorporatingthe force-measuring device, and calibrating the force-measuring deviceor mapping data of force transmission to the force-measuring device. Atstep 552, the CMOS wafer is fabricated using a semiconductor substrate.This step has been described with reference to FIG. 17. At step 562, aMEMS wafer is fabricated using a MEMS substrate, such as silicon orglass. Step 562 includes the fabrication of PFMEs (more generally, MEMSstructures). At step 564, the CMOS wafer and the MEMS wafer are attachedby wafer bonding, resulting in the semiconductor substrate and the MEMSsubstrate being attached to each other at their major surfaces. At step566, the force-measuring devices (270) are made. This step 566 includes,for example, the singulation of the bonded wafer into dies, the mountingof dies onto a package substrate, and the packaging of the die includingapplication of an epoxy adhesive. The making of the force-measuringdevice is complete at the end of step 566. At step 566, theforce-measuring devices (270) are optionally incorporated into anelectronic apparatus (640), as explained with reference to FIG. 17. Atstep 568, the force-measuring device undergoes calibration, either inits standalone state or after incorporation into an electronicapparatus, according to method 800 (FIG. 28) or a mapping of data offorce transmission from a plurality of force-imparting points to theforce-measurement device is obtained according to method 870 (FIG. 31).

FIG. 19 shows a flow diagram of a method 570 of making force-measuringdevice (280 of FIG. 12), making an electronic apparatus incorporatingthe force-measuring device, and calibrating the force-measuring deviceor mapping data of force transmission to the force-measuring device. Atstep 572, a MEMS wafer is fabricated using a MEMS substrate, such assilicon or glass. Step 572 includes the fabrication of PFMEs (moregenerally, MEMS structures). At step 576, the MEMS chips (280) are made.This step 576 includes, for example, the singulation of the MEMS waferinto dies, the mounting of dies onto a package substrate, and thepackaging of the die including application of an epoxy adhesive. Sincethe MEMS device 280 does not include the signal processing circuitry,the signal processing circuitry is provided in other ICs. At step 576,the MEMS device is electronically coupled to the signal processingcircuitry. Upon completion of step 576, the MEMS device 280 has beenconfigured as a force-measuring device. At step 576, the force-measuringdevices (280) are optionally incorporated into an electronic apparatus(640), as explained with reference to FIG. 17. At step 578, theforce-measuring device, either in its standalone state or afterincorporation into an electronic apparatus, undergoes calibration,namely the method 800 (FIG. 28). At step 578, the force-measuring deviceundergoes calibration, either in its standalone state or afterincorporation into an electronic apparatus, according to method 800(FIG. 28) or a mapping of data of force transmission from a plurality offorce-imparting points to the force-measurement device is obtainedaccording to method 870 (FIG. 31).

What is claimed is:
 1. A force-measuring device testing system,comprising: a linear actuator assembly comprising a Z-axis actuator anda slider; a load cell secured to the slider, such that actuation of theZ-axis actuator is mechanically coupled to a vertical movement of theload cell via the slider; a sample stage configured to retain a samplecomprising a force-measuring device; a controller electronically coupledto the Z-axis actuator; and a load cell signal processing circuitryelectronically coupled to the load cell and the controller, configuredto measure force signals at the load cell and output amplified forcesignals to the controller; wherein the load cell is configured, in aforce-imparting mode, to impart a time-varying applied force to thesample during the vertical movement of the load cell, the time-varyingapplied force being imparted via at least one elastic member positionedbetween the load cell and the sample; and the controller is configured,in the force-imparting mode, to repeatedly carry out the following untila desired force trajectory has been executed: (1) calculate digitalforce signals in accordance with the amplified force signals, (2)calculate a next actuation of the Z-axis actuator in accordance with thedesired force trajectory and an elastic parameter, and (3) control theactuation of the Z-axis actuator in accordance with its next calculatedactuation, wherein the elastic parameter relates actuation of the Z-axisactuator to digital force signals resulting from the actuation.
 2. Theforce-measuring device testing system of claim 1, wherein the controlleris configured to update the elastic parameter in accordance with adeviation of the digital force signals from the desired forcetrajectory.
 3. The force-measuring device testing system of claim 1,wherein the sample stage comprises a sample stage positioner, thecontroller electronically coupled to the sample stage positioner.
 4. Theforce-measuring device testing system claim 1, wherein: the sample is anelectronic apparatus; and the electronic apparatus comprises amicroprocessor and a memory electronically coupled to themicroprocessor.
 5. The force-measuring device testing system of claim 1,wherein the force-measuring device is a packaged integrated circuit. 6.The force-measuring device testing system of claim 5, wherein theforce-measuring device comprises piezoelectric micromechanicalforce-measuring elements (PMFEs).
 7. The force-measuring device testingsystem of claim 1, wherein the Z-axis actuator comprises a steppermotor.
 8. The force-measuring device testing system of claim 1, whereinthe load cell signal processing circuitry comprises an instrumentationamplifier.
 9. The force-measuring device testing system of claim 1,wherein the load cell is a first load cell and the force-measuringdevice testing system additionally comprises a second load cell securedto the slider, such that actuation of the Z-axis actuator ismechanically coupled to a vertical movement of the second load cell viathe slider, the first load cell and the second load cell being orientedin opposite directions along a vertical axis, the load cell signalprocessing circuitry being electronically coupled to the second loadcell.
 10. The force-measuring device testing system of claim 9, wherein:the force signals are first force signals; the amplified force signalsare first amplified force signals; the load cell signal processingcircuitry is configured to measure second force signals at the secondload cell and output second amplified force signals to the controller.11. The force-measuring device testing system of claim 10, wherein thecontroller is configured to convert the first amplified force signals tofirst digital force signals, convert the second amplified force signalsto second digital force signals, and subtract the second digital forcesignals from the first digital force signals to obtain the digital forcesignals.
 12. The force-measuring device testing system of claim 10,wherein: the first load cell, the second load cell, and the slider areconfigured to be stationary during a manual input mode; the second loadcell is configured, during the manual input mode, to receive manualforce input, the manual force input being measurable as second forcesignals at the second load cell; the controller is configured, in themanual input mode, to: (1) calculate digital force signals in accordancewith the second amplified force signals and (2) determine the desiredforce trajectory in accordance with the digital force signals.
 13. Theforce-measuring device testing system of claim 1, wherein the at leastone elastic member comprises a first elastic member and a second elasticmember, the first elastic member and the second elastic member beingarranged in series between the load cell and the sample.
 14. Theforce-measuring device testing system of claim 13, wherein first elasticmember is less elastic than the second elastic member.
 15. Theforce-measuring device testing system of claim 13, wherein the firstelastic member comprises a spring.
 16. The force-measuring devicetesting system of claim 13, wherein second elastic member comprises arubber block.
 17. A force-measuring device calibration system,comprising: a linear actuator assembly comprising a Z-axis actuator anda slider; a load cell secured to the slider, such that actuation of theZ-axis actuator is mechanically coupled to a vertical movement of theload cell via the slider; a sample stage configured to retain a samplecomprising a force-measuring device, each force-measuring devicecomprising a signal processing circuitry; a controller electronicallycoupled to the Z-axis actuator; a load cell signal processing circuitryelectronically coupled to the load cell and the controller, configuredto measure force signals at the load cell and output amplified forcesignals to the controller; and a force-measuring device controllerelectronically coupled to the signal processing circuitry of eachforce-measuring device; wherein the load cell is configured, in aforce-imparting mode, to impart a time-varying applied force to thesample during the vertical movement of the load cell, the time-varyingapplied force being imparted via at least one elastic member positionedbetween the load cell and the sample; the controller is configured, inthe force-imparting mode, to repeatedly carry out the following until adesired force trajectory has been executed: (1) calculate digital forcesignals in accordance with the amplified force signals, (2) calculate anext actuation of the Z-axis actuator in accordance with the desiredforce trajectory and an elastic parameter; and (3) control the actuationof the Z-axis actuator in accordance with its next calculated actuation,the elastic parameter relating actuation of the Z-axis actuator todigital force signals resulting from the actuation; and theforce-measuring device controller is configured to: (1) read digitaltransducer data output from the signal processing circuitry of theforce-measuring device(s) when the time-varying applied force isimparted to the sample, and (2) adjust or select a gain of theforce-measuring device(s) in accordance with the digital transducerdata.
 18. The force-measuring device calibration system of claim 17,wherein the controller is configured to update the elastic parameter inaccordance with a deviation of the digital force signals from thedesired force trajectory.
 19. The force-measuring device calibrationsystem of claim 17, wherein the sample stage comprises a sample stagepositioner, the controller electronically coupled to the sample stagepositioner.
 20. The force-measuring device calibration system of claim17, wherein: the sample is an electronic apparatus; the electronicapparatus comprises a microprocessor and a memory electronically coupledto the microprocessor; and the microprocessor functions as theforce-measuring device controller.
 21. The force-measuring devicecalibration system of claim 17, wherein the force-measuring devicecontroller is configured to calculate calibration data and store thecalibration data in the force-measuring device.
 22. The force-measuringdevice calibration system of claim 21, wherein the calibration datacomprises: (1) a ratio of a characteristic amplitude of the digitaltransducer data to a characteristic amplitude of the digital forcesignals, or (2) a ratio of a characteristic amplitude of the digitalforce signals to a characteristic amplitude of the digital transducerdata.
 23. The force-measuring device calibration system of claim 17,wherein the force-measuring device is a packaged integrated circuit. 24.The force-measuring device calibration system of claim 23, wherein theforce-measuring device comprises piezoelectric micromechanicalforce-measuring elements (PMFEs).
 25. The force-measuring devicecalibration system of claim 17, wherein the Z-axis actuator comprises astepper motor.
 26. The force-measuring device calibration system ofclaim 17, wherein the load cell signal processing circuitry comprises aninstrumentation amplifier.
 27. The force-measuring device calibrationsystem of claim 17, wherein the load cell is a first load cell and theforce-measuring device calibration system additionally comprises asecond load cell secured to the slider, such that actuation of theZ-axis actuator is mechanically coupled to a vertical movement of thesecond load cell via the slider, the first load cell and the second loadcell being oriented in opposite directions along a vertical axis, theload cell signal processing circuitry being electronically coupled tothe second load cell.
 28. The force-measuring device calibration systemof claim 27, wherein: the force signals are first force signals; theamplified force signals are first amplified force signals; and the loadcell signal processing circuitry is configured to measure second forcesignals at the second load cell and output second amplified forcesignals to the controller.
 29. The force-measuring device calibrationsystem of claim 28, wherein the controller is configured to convert thefirst amplified force signals to first digital force signals, convertthe second amplified force signals to second digital force signals, andsubtract the second digital force signals from the first digital forcesignals to obtain the digital force signals.
 30. The force-measuringdevice calibration system of claim 17, wherein: the first load cell, thesecond load cell, and the slider are configured to be stationary duringa manual input mode; the second load cell is configured, during themanual input mode, to receive manual force input, the manual force inputbeing measurable as second force signals at the second load cell; andthe controller is configured, in the manual input mode, to: (1) obtaindigital force signals in accordance with the second amplified forcesignals and (2) determine the desired force trajectory in accordancewith the digital force signals.
 31. The force-measuring devicecalibration system of claim 17, wherein the at least one elastic membercomprises a first elastic member and a second elastic member, the firstelastic member and the second elastic member being arranged in seriesbetween the load cell and the force-measuring device.
 32. Theforce-measuring device calibration system of claim 31, wherein firstelastic member is less elastic than the second elastic member.
 33. Theforce-measuring device calibration system of claim 31, wherein the firstelastic member comprises a spring.
 34. The force-measuring devicecalibration apparatus of claim 31, wherein second elastic membercomprises a rubber block.
 35. A force-imparting system, comprising: alinear actuator assembly comprising a Z-axis actuator and a slider; aload cell secured to the slider, such that actuation of the Z-axisactuator is mechanically coupled to a vertical movement of the load cellvia the slider; a sample stage configured to retain a sample; acontroller electronically coupled to the Z-axis actuator; and a loadcell signal processing circuitry electronically coupled to the load celland the controller, configured to measure force signals at the load celland output amplified force signals to the controller; wherein the loadcell is configured, in a force-imparting mode, to impart a time-varyingapplied force to the sample during the vertical movement of the loadcell, the time-varying applied force being imparted via at least oneelastic member positioned between the load cell and the sample; and thecontroller is configured to repeatedly carry out the following until adesired force trajectory has been executed: (1) calculate digital forcesignals in accordance with the amplified force signals, (2) update anelastic parameter in accordance with a deviation of the digital forcesignals from a desired force trajectory, (3) calculate a next actuationof the Z-axis actuator in accordance with the desired force trajectoryand the updated elastic parameter; and (4) control the actuation of theZ-axis actuator in accordance with its next calculated actuation, theelastic parameter relating actuation of the Z-axis actuator to digitalforce signals resulting from the actuation.
 36. The force-impartingsystem of claim 35, wherein the load cell is a first load cell and theforce-imparting system additionally comprises a second load cell securedto the slider, such that actuation of the Z-axis actuator ismechanically coupled to a vertical movement of the second load cell viathe slider, the first load cell and the second load cell being orientedin opposite directions along a vertical axis, the load cell signalprocessing circuitry being electronically coupled to the second loadcell.
 37. The force-imparting system of claim 36, wherein: the forcesignals are first force signals; the amplified force signals are firstamplified force signals; and the load cell signal processing circuitryis configured to measure second force signals at the second load celland output second amplified force signals to the controller.
 38. Theforce-imparting system of claim 37, wherein the controller is configuredto convert the first amplified force signals to first digital forcesignals, convert the second amplified force signals to second digitalforce signals, and subtract the second digital force signals from thefirst digital force signals to obtain the digital force signals.
 39. Theforce-imparting system of claim 37, wherein: the first load cell, thesecond load cell, and the slider are configured to be stationary duringa manual input mode; the second load cell is configured, during themanual input mode, to receive manual force input, the manual force inputbeing measurable as second force signals at the second load cell; andthe controller is configured, in the manual input mode, to: (1)calculate digital force signals in accordance with the second amplifiedforce signals, and (2) determine the desired force trajectory inaccordance with the digital force signals.
 40. A method of calibrating aforce-measuring device, comprising the steps of: (A) configuring aforce-measuring device testing system, comprising: (1) a linear actuatorassembly comprising a Z-axis actuator and a slider, (2) a load cellsecured to the slider, such that actuation of the Z-axis actuator ismechanically coupled to a vertical movement of the load cell via theslider, (3) a controller electronically coupled to the Z-axis actuator,and (4) a load cell signal processing circuitry electronically coupledto the load cell and the controller, configured to measure force signalsat the load cell and output amplified force signals to the controller;(B) configuring a sample stage, a sample comprising a force-measuringdevice, and a force-measuring device controller, the sample stageretaining the sample, each force-measuring device comprising a signalprocessing circuitry, the force-measuring device controllerelectronically coupled to the signal processing circuitry of eachforce-measuring device; (C) obtaining a desired force-trajectory; (D)operating the force-measuring device testing system; (E) reading, by theforce-measuring device controller, a digital transducer data output froma signal processing circuitry of the force-measuring device when thetime-varying applied force is imparted to the sample; and (F) adjustingor selecting, by the force-measuring device controller, a gain of theforce-measuring device in accordance with the digital transducer data;wherein the step (D) of operating the force-measuring device testingsystem comprises the sub-steps of: (D1) calculating, by the controller,an actuation of the Z-axis actuator in accordance with the desired forcetrajectory and an elastic parameter; (D2) controlling, by thecontroller, actuation of the Z-axis actuator in accordance with thecalculated actuation; (D3) imparting, by the load cell, a time-varyingapplied force to the sample during the vertical movement of the loadcell, the time-varying applied force being imparted via at least oneelastic member positioned between the load cell and the sample; (D4)measuring, by the load cell signal processing circuitry, force signalsat the load cell and amplifying the force signals; (D5) outputting, bythe load cell signal processing circuitry, amplified force signals tothe controller; (D6) obtaining, by the controller, digital force signalsin accordance with the amplified force signals; (D7) optionallyupdating, by the controller, the elastic parameter in accordance with adeviation of the digital force signals from the desired forcetrajectory; and (D8) repeatedly executing steps (D1) through (D7),inclusive, until the desired force trajectory has been executed; andwherein the elastic parameter relates actuation of the Z-axis actuatorto digital force signals resulting from the actuation.
 41. The method ofclaim 40, additionally comprising: (G) calculating, by theforce-measuring device controller, calibration data; and (H) storing, bythe force-measuring device controller, the calibration data in theforce-measuring device.
 42. The method of claim 41, wherein thecalibration data comprises: (1) a ratio of a characteristic amplitude ofthe digital transducer data to a characteristic amplitude of the digitalforce signals; or (2) a ratio of a characteristic amplitude of thedigital force signals to a characteristic amplitude of the digitaltransducer data.
 43. The method of claim 40, wherein: the sample is anelectronic apparatus; the electronic apparatus comprises amicroprocessor and a memory electronically coupled to themicroprocessor; and the microprocessor functions as the force-measuringdevice controller.
 44. The method of claim 40, wherein theforce-measuring device is a packaged integrated circuit.
 45. The methodof claim 44, wherein the force-measuring device comprises piezoelectricmicromechanical force-measuring elements (PMFEs).
 46. The method ofclaim 40, wherein the Z-axis actuator comprises a stepper motor.
 47. Themethod of claim 40, wherein the load cell signal processing circuitrycomprises an instrumentation amplifier.
 48. The method of claim 40,wherein: the load cell is a first load cell; the force signals are firstforce signals; the amplified force signals are first amplified forcesignals; the force-measuring device testing system additionallycomprises: a second load cell secured to the slider, such that actuationof the Z-axis actuator is mechanically coupled to a vertical movement ofthe second load cell via the slider, the first load cell and the secondload cell being oriented in opposite directions along a vertical axis;and the load cell signal processing circuitry is electronically coupledto the second load cell, configured to measure force signals at thesecond load cell and output second amplified force signals to thecontroller.
 49. The method of claim 48, wherein: the sub-step (D4)additionally comprises: measuring, by the load cell signal processingcircuitry, second force signals at the second load cell and amplifyingthe second force signals; and the sub-step (D5) additionally comprises:outputting, by the load cell signal processing circuitry, secondamplified force signals to the controller.
 50. The method of claim 49,wherein the sub-step (D6) comprises: converting the first amplifiedforce signals to first digital force signals, converting the secondamplified force signals to second digital force signals, and subtractingthe second digital force signals from the first digital force signals toobtain the digital force signals.
 51. The method of claim 48, whereinthe step (C) of obtaining a desired force-trajectory comprises thesub-steps of: (C1) receiving, by the second load cell, a manual forceinput while the first load cell, the second load cell, and the sliderare configured to be stationary during a manual input mode; (C2)measuring, by the load cell signal processing circuitry, second forcesignals at the second load cell and amplifying the second force signals;(C3) outputting, by the load cell signal processing circuitry, secondamplified force signals to the controller; (C4) obtaining, by thecontroller, digital force signals in accordance with the secondamplified force signals; and (C5) determining, by the controller, thedesired force trajectory in accordance with the digital force signals.52. The method of claim 40, wherein the at least one elastic membercomprises a first elastic member and a second elastic member, the firstelastic member and the second elastic member being arranged in seriesbetween the load cell and the force-measuring device.
 53. The method ofclaim 52, wherein first elastic member is less elastic than the secondelastic member.
 54. The method of claim 52, wherein the first elasticmember comprises a spring.
 55. The method of claim 52, wherein secondelastic member comprises a rubber block.